Its a touch heavy on memory (60MB per window - the coding still needs optimizing), but its not at all noticeable when using the browser - its still way faster then FF and IE. And best of all it doesnt impact at all on the performance on the PC, so whilst its heavy on memory, its not actually leaking memory like both IE and FF are guilty of doing.
Some people have had issues running it on Vista, but Apple have said its coded for XP with Vista taking second priority atm as XP is more commonplace. Having said that, some people have had issues running it on XP (as in it sometimes doesnt show the menus correctly) but im running it totally fine.
Im not 100% convinced by the interface, its a bit too minimalist imho, especially as I am used to that of IE, but one cannot get way from the sheer phenominal speed of the page loading and quality of the page rendering, FF and IE don't even come close to it. The AA text is really neat too, sometimes it looks a little too bold, but 99% of the time its fine.
Overall, I am impressed, and can see why mac users have raved about it for years. And at the end of the day, even if I decide not to take it up full time (still 50/50 about leaving IE) its a great tool for web developing.
It will only get better as the BETA is improved and more plugins are released by both Apple and 3rd party developers.