That's odd Ziggie, I've imported three pz3's, two from P6 and one from P5 and have had no troubles.  Heck, one is my most recent gallery posting, the pic locked up P6 about a third of the way through the render, P7 did the whole picture in under 2 hours!  (Full IBL AO, raytracing at 1600X1200 on an AMD 2600 with 1.25GB RAM)  Not too shabby.

Still, I'd be curious to hear about other people's encounters with bugs.

Now to think of it, while I was playing earlier today I did manage to crash it, but I figured it was my own fault.  I put a 150 frame walk designer animation on V4, then tried to add a Universal Pose motion capture at the end.  Whole system locked up and stopped responding.  I just figured I did something wrong.