I like it..Can be cranky at times when I try to do some 'different' types of designs..I am running it on Win XP-Pro, have heard some people have problems running it on VISTA..All in all a very versatile and valuable software program to have.
I never used the previous versions but I have version 9 on Vista (x64 even) and it runs mostly fine. I had it crash once when I opened it for no apparent reason, but other than that one time, it's been fine.
I'm running it on a MAC and it's great. Be careful, it is addicting. I noticed a few glitches: Can't add some parts to the database by hand, sometimes a window must be moved slightly to allow activity. If you have never used Rocksim before be sure to check out all the videos on the Apogee website.