After installing the 1.8 update MC stopped working, when i try to load a world (or start a new one) it just goes to a black screen. I even deleted MC and reinstalled the entire thing and it still won't work.
I have the same problem and i use a MAC. I looked around on the internet and a lot of people using MAC are having the problem. It seems the video component that is required by the 1.8 update is higher than what MAC OS-X is. Meaning if you're using a MAC OS-X you'll need to upgrade to the Snow Leopard, which is like $30.00, and as far as i've seen cannot be downloaded off the internet, so youd need it shipped to you, or buy it at the store =/
OR Notch might fix it so MAC-OSX can run minecraft again, like it always has ;o