I have this problem as well. It only seems to occur when I'm working within a certain area of the map. If I exit minecraft from another location I don't have that issue. After force-closing minecraft a few times after getting stuck on the "Downloading terrain" map, I just let it run until something happened and minecraft crashed. I have uploaded the attached crash report.
DANIEL RAMIREZ
I have this problem as well. It only seems to occur when I'm working within a certain area of the map. If I exit minecraft from another location I don't have that issue. After force-closing minecraft a few times after getting stuck on the "Downloading terrain" map, I just let it run until something happened and minecraft crashed. I have uploaded the attached crash report.