I recently upgraded to Gentoo 64 bit and generally it's been great. Dropped LVM and just used partitions at the same time and it feels generally a bit quicker. A few issues with Steam but they've been resolved in another post.
Minecraft was the one thing that still didn't work.
It needed one extra install to make it work.
emerge x11-apps/xrandr
Once this was installed it worked fine otherwise it crashes with errors like:
OpenGL: ~~ERROR~~ RuntimeException: No OpenGL context found in the current thread.
