I've played around with it for a few minutes, my initial thoughts:
Best looking browser, hands down.
Very quick, impressive.
Do we really need another browser?
I miss my Firefox Plugins. Essential to daily use.
If Apple were smart, I think they'd make Safari backwards compatible with Firefox's Add-On's structure, so that I keep my plugins. Not sure if this is possible on a technical level, but it's crucial in my opinion to courting a huge sector technical and non-technical people alike.