Installed 4 two days ago. In about 16 hours of editing I Had a bunch of actions stop working, crashes and BSODs. (64bit version on 64 bit Win 7 with 64 bit version of SWS)
I really dislike what they've done with the floating toolbars. Also when I've got my slice tool armed sometimes clicking on the ruler to move the cursor will cut across all tracks (worst case), or the playhead will not visually move (bug?) not how it used to work.
I guess I'll go back to V3 32bit for a while.