Much has been written about PlayBook stability, mainly from journalists with pre-release versions. My experience has been much better after 5 days of heavy use. I had a crash on day one - and nothing since then. Well not quite. Yesterday, when I let relatives visit their favorite sites, the browser would repeatedly quit. Then I tried and got the same results on sites that worked well days before. I had not booted my PB for 3 days. One restart yesterday fixed the problem. We geeks don't generally believe in the boogey man and know this is a good sign of memory leaks. We also know it will be fixed in short order. It's fair to say the PB is about as stable as my first generation iPhone.
Late last night a 250+ MB OS update was pushed to my PlayBook. It will undoubtedly have the first of many memory and performance fixes.