So far I don't mind the hiccups we have to deal with playing SSP as if it were SMP. It is small potatoes.
Tonight I was unable to log into Minecraft.net to play the game, so I had to play it offline. That is fine, too.
However, I loaded up my world, and found myself at my default spawn with no items in my inventory, and a cow staring at me asking what the hell I was doing there. I was asking the same question as I distinctly remembered closing down my game the other night with a well-stocked inventory of tools and sitting in my house of stone.
So, basically, if you or Mojang have an issue with being online, then anything you had in your inventory in the world you choose to load up will be erased from existence and you could end up very far away from your last location. I find that one problem with this new arrangement that needs to be addressed. True you can save a chest to store your inventory in when you log off as a safeguard against having to play offline the next time, but also losing your last saved spawn position can end up a worse condition.
You could also choose to treat not being able to log in as an Error 37 and choose not to log in at all, therefore avoiding changing your current world. That's just screwed up in its own way. Playing SSP shouldn't be affected by whether you are online or off.
We best be a long ways off before implementing this new change as a full update. Otherwise I won't be updating again.
Rollback Post to RevisionRollBack
In the real world, you stick your head in the dirt to hide from problems.
In Minecraft, you stick your head in the dirt to find problems.
So, basically, if you or Mojang have an issue with being online, then anything you had in your inventory in the world you choose to load up will be erased from existence and you could end up very far away from your last location.
Not erased from existence at all. When you play offline, you're not "Samsonguy920" (or whatever your MC name is) anymore, you're "Player". The next time you're able to play online, you'll be you again, with all your inventory, and standing right where you left yourself when you were last "online".
BTW, I wouldn't keep anything important in your inventory while you're "Player", if I were you. That may or may not be a temporary inventory that could get erased. Either way, you won't have access to "Player's" inventory anymore once you're logged in.
Anyway, as -Freshmeat said, this is a known bug that came with the merge, and Mojang most likely knows about it already. I wouldn't be surprised if the Bukkit guys have already fixed it.