In the latest 3D World magazine (great, expensive but worth it), issue 136, December 2010, there is a preview of Modo 501 (article, not a software trial) and an interview with Brad Peebler.
Three big things that are talked about in 501 are Pixar Sub D (PSUB) modeling, Multi-Resolution Sculpting (very Zbrush like) and the very cool sounding RayGL display. The latter allows you to model in a raytraced view. This is different from the preview render which also has improvements.
Mac 64bit OSX has been confirmed.
Also, much ado about redone bump and displacement mapping, snapping, much faster render speeds, etc.
Definitely no character animation in this release, maybe 601 (maybe).
Also, they say late November release (but not confirmed).
Looks very cool but this release (501) is all about fixing problems with previous releases for improved stability, speed and workflow.