I've been using Premiere CS3 on the Mac for about a year now, and while functionally it works just fine I have random crashes CONSTANTLY. If I look at the screen the wrong way, it seems to crash for no apparent reason at all.
Not to get into troubleshooting my setup (a top of the line Mac Pro, I've wiped the computer clean at least once and reinstalled CS3 many times, blah blah blah)--any of you out there who have had similar problems with CS3--in general, have you found CS4 to be more reliable?
While I find it ridiculous that I have to upgrade just to make the software I paid for stop crashing so much, I'd do it if it means fewer frustrations getting my work done.
In my experience, yes CS4 is much better on the Mac. I have a Mac Pro with 16 GB RAM and Premiere Pro is very fast. My only caveat is that you don't want to import a CS3 project into CS4. The conversion process doesn't seem to work properly (at least on the Mac) and performance will be sluggish. Start with a fresh CS4 project though and you will find performance is excellent.