From what little I’ve used if it so far, I’m impressed. I’m using 8.00 BETA at the moment, so I can’t really comment on the stability of the final release, but the beta is pretty stable. I can already see a couple of rendering bugs (but thats caused by sloppy CSS from the WordPress Admin pages). It renders this site without much fault though (apart from a few margin issues at the top and bottom, which I’ll fix later).
The free version of Opera has adverts, although for some reason, my remains blank. I think it might have to do with ZoneAlarm on my system blocking the ads, although I’ll get back to you on that issue.