Ran a survival world in the prerelease for awhile, when it started crashing on me all of a sudden. Was able to ascertain that it only happened when I walked beyond certain boundaries (possibly chunk-related?).
Tried updating Java
Tried wiping my .Minecraft, and putting the world back in.
Attached is the error report. I would've also attached my world directly, but it exceeds the 10.00 MB attachment limit (it's 15.87 MB)
I have instead uploaded it to MediaFire. You may download it from the following link.