Well I've been playing with the Safari 4 beta on the mac. And I have to say I'm impressed with what they've done.
it's faster than Firefox 3.0 on my Mac. And combined with the fact that Safari now has an Adblock plug-in (at least for the mac), I'm afraid to say I'm probably jumping ship until Firefox releases something better.
I haven't tried Safari 4 Beta on the PC but it's supposed to be much better.
http://www.apple.com/safari/
EDIT: for the web developer this is a MUST! It has included developer features like you wouldn't believe!
• The ability to emulate any browser's user agent for compatibility checks. (this doesn't seem to work perfectly)
• Web Inspector window for code check, CSS check.
• See EXACTLY how long elements took to load.
• The list goes on and on!
