It's only been a day, but I'm really liking OmniWeb 5. I had one crash, but other than that it's been flawless.
The extra features are great (edit HTML then refresh the browser window - on any website!). Love the thumbnail tab view. Love the speed and ad-blocking. Hate the lack of Safari's cool progress bar. Hate the separate Reload and Stop buttons. Hate that GMail doesn't work in it... I did pay my upgrade fee for OW5 already, though ;-)