While downgrading "worked" fairly well the last few versions (except the missing blocks and things like that), downgrading does not work in 1.8! If you downgrade from 1.8 to 1.7, your inventory and all blocks with an inventory (chests, hoppers etc.) will be empty and potentially, even more corruption is happening. Downgrading is not, was never and will never be officially supported! I advise you to run 1.8 in a seperate directory, or move your 1.7 things to a different one, so that you won't be able to accidently open your world in the wrong version.
If you already did it, by accident or "on purpose", restore a backup or find other ways to restore the items (e.g. via using Creative to give them back from memory), other than that, there is no way to repair this.
2. Name changing
Changing your name will NOT be possible immediately after the release of 1.8! It is currently planned "soon-ish" after 1.8, /u/Marc_IRL's statement about this can be found here.
3. Water Temple, New Stones and Rabbits
This upcoming update adds some new features for the world generator, but specifically, they added Retrogen (Retroactive World Generation) for the brand new underwater temples: If you have spent less than a specific amount of time in the chunks the temple would normally spawn, it also spawns in already generated Ocean Biomes. Additionally, it seems that older worlds (1.7 and earlier) are spawning Guardians where normally a temple would have spawned.
However, this only works for the Underwater Temples, the new types of stones and rabbits only spawn in chunks generated in 1.8. However, there are crafting recipes for the stones, which can all be found here.
Skins received a massive update: You can now have a second layer for your whole body. /u/Svajoklis_ provided a very nice guide on how to upgrade your skin: Guide. However, you don't need to update your skin, you can still use the one you had before 1.8.
Slimmer arms (3 pixel wide) will not be available as a feature in the full 1.8 release, Jeb said that "it will be rolled out independently of Minecraft version numbers".
More information about Skins can be found here.
5. New graphical settings
Some graphical settings have changed, new ones have been added and other ones have been removed.
Enabling VBOs (Vertex Buffer Objects) can give you a performance boost or a drop, just try it out yourself.
Regarding the Render Distance: 32 chunks are only available if you are assigning 2GB or more RAM to Minecraft, however, I personally recommend at least 4GB. Don't even try it with an Intel Graphics Card, it will not/barely work. Most AMD cards have a problem with anything higher than 16, but that is most likely an issue on AMD's side (MC-62958). On Nvidia Cards, it seems to run fine (if they have the power to do it, GT 650M can run it at about 15-20 FPS with major lag spikes).
Anisotropic Filtering has been removed because of reasons unknown, Advanced OpenGL was just causing major problems, and was therefore removed.
6. Enchanting and Repairing
Enchanting and Repairing have been both massively changed from 1.7 to 1.8.
Enchanting: Using the enchantment table only uses 1-3 levels, however, you still need to have the amount of levels it shows on the right side. Additionally, it costs Lapis Lazuli to enchant something (1-3, depending on how many levels you spend). Also, available enchantments no longer change if item is taken out and put back in, and enchanting something changes the available enchantments for all items, and it's the same for every enchantment table with the same amount of books in that world.
Repairing: The level cost for all is starting at 1, and goes up exponentially with every time you use it in the Anvil. For instance, just renaming something costs 1 level, but if you rename it and then apply an enchanting it with a book, it costs one level for the renaming and two for the enchanting. Also, repairing costs can no longer be kept down by renaming items. (This explanation might have been terrible, if you have issues understanding it, ask your question in the comments)
Maps changed (not actual save games, I'm talking about the In-Game Item). This might be a bug, at least it has been reported as such, but this looks like intended behavior. Basically: If you create a map with at least 1:2 in 1.8, it will not be centered to the point you are at at the moment of creation, it will be patterned like the 1:1 always was. That makes it easier to make multiple maps for a map wall, because it doesn't require any calculating, but people seem to not like the new mechanic. There has not been an official comment from Mojang on this matter.
8. Is this Release stable?
There are some very minor issues that can break things (for instance: Two high flowers do not properly update from 1.7 to 1.8), but all in all, they ironed out most of the last few world breaking bugs in the last Snapshots, and it's now in a very much playable state.
Some bugs you may want to know about can be found as the first comment of this PSA.
9. Resource Packs
Resourcepacks require an update to work, since a few textures changed (e.g. enchantment table), but they don't break/crash if you use a 1.7 pack on 1.8.
Remember how 1.8 was supposed to increase performance fairly greatly? Well, for me, I lag 10x more than I did in 1.7.10, even after turning all my settings down. I lag like crazy, especially on Realms.
Ever since 1.8 was released, the game freezes constantly and is unplayable. Since there doesn't seem to be a way to contact Mojang directly for tech support (mineceraft.net tells me to go here for help), I need someone to help me fix this, or revert back to the previous version I was using before this forced upgrade.
I think this should be added to the sticky, it took me forever to find a solution to why my 1.7 to 1.8 made a dramatic loss in FPS. I learned that 1.8 is the first time it can use 64bit java. Since my OS is 64 Bit, this was the critical change. I had to uninstall the 32 bit version, and install the 64 bit java (which java.com seems to want to avoid because of IE). Once i rebooted and only had 64bit java, the game is epicly fast and smooth. We need to spread the word about this.
its not minecraft that needs a 64 bit java it was your computer if youre running 64 bit then everything you run that can do 64 bit should be ran like that. 32 bit systems can not run 64 bit software. therefore anyone with a 32 bit OS will run into problems when trying this so called solution.
Rollback Post to RevisionRollBack
the earth first! we can strip mine the rest of the universe after. click the up arrow if i helped.
Have you tried to download the 64 bit java? Try, its practically hidden on their site, after you follow their run-around. I'm a pretty decent PC user, and never once thought that i would have to snoop around Java.com to find the right version for my OS. I falsely assumed like most people that the big red Agree and Start Download button would be correct option.
This fixed my problem and same for 3 friends, I know we are not the only ones. Just wanted to help spread the word.
My minecraft breaks when i load a texturepack i didn`t have when i loaded minecraft. is this just for people with a steve skin model or me or everyone. Also on hardcore i lost because i could mine a freaking block. I would mine it and it would place it self back again and then i would repeat and the same thing happens.
I came here to find a solution to this bug, but i guess i'll just be giving my items back, i almost died when all my stuff were gone(literal sense, terrible accident), and they really need to fix this, :/
For some reason my Minecraft will not open and keeps crashing. I think it has something to do with my driver. I followed some basic instructions and got to this. Can you please tell me what my problem is and help me to fix it?
Titantstayer You probably have too many things on your computer and need to delete unimportant things. Or it could be your computer is BAD. My computer has the same problem if I'm trying to load in too many things in a single player world.
The Meaning of Life, the Universe, and Everything.
North Carolina, USA
It's probably pointless to mention this now that 1.9 is literally around the corner, however, rabbits do spawn in old chunks. I've found several in the area surrounding my home/spawn in my 1.7 world, which I had explored for thousands of blocks around prior to 1.8's release, so they're not from new chunks. I'm guessing they are part of the extremely rare post-generation spawns.