In the recent snapshot, there is an unbelievable amount of lag. In 1.6, I usually get around 60fps. In snapshot 13w36a (and b), I got around 30fps (maximized), but now I am getting between 0 and 7 fps. The game is unplayable, even with all settings turned down.
I also have noticed that the Super Secret Settings button does nothing. I've tried, the shader won't change.
Linked issues
Comments 4

Can you attach your game settings here please?
Link to crash: http://pastebin.com/QTs23fr4
@Kyle Applin: Game settings?
Please force a crash by pressing F3 + C for 10 seconds while in-game and attach the crash report (
[minecraft|http://hopper.minecraft.net/help/finding-minecraft-data-folder]/crash-reports/crash-<DATE>-client.txt
) here.