On my mac I've discovered that certain sites cause problems with Safari. Usually it's due to bad programming in the animated advertisements. Which I was hoping the absence of Flash and Java would actually make things more stable.
The same thing was happening to me in the APPLE store in Boca Raton, FL. I was able to pry a iPhone away from some 8 year old kid and after surfing on their WiFi for about thirty mins I had numerous Safari shutdowns too. I figued i was doing something wrong but after reading this post i guess not. I was wondering if maybe i lost connection to the network or something. Oh well. I hope they get this issued ironed out by the time i buy a Version 2 with EDGE.