I'm currently using build 686 with Java DP6. Actually for the first time IDEA 3 is usable under OS X...
Besides the keyboard mapping problems I already had with version 2.6, V3 has added some more: the < and + characters vanished. Most interestingly the same keys shifted do work (> and * are no problem).
Besides that popup windows tend to stay on screen (e.g. after clicking on the yellow light bulb). Popup menus (right click) disappear immediatly when the menu is near the screen border (guess this is an Apple JDK problem).
When adding files to the CVS repository, cvs complains that I should login first (I am using a pserver repository). I did login on the commandline outside IDEA and could not find any way to do that from within IDEA.
Performace is quite good on my dual G4. All in all it looks quite promising now.