I've been using the Preview Release for a couple months now. Cons - can have occaisonaly weird formatting issues, occaisonal browser compatibility issues (AlaskaAir's website), pages with alot of images can load weird. I find I use it about 90% of the time now at home (work won't allow me to install it )
Pluses - In Browser search engines - several hundred different engine plugins available for it (those mentioned above, amazon, eBay, wikipedia, lots more), found firefox will load BB's like cc if ie is choking on them, pop up control, tabbed browsing .
I only used a couple of the earlier versions of Opera. Overall this seems a much better implementation of some of the earlier Opera ideas like tabbed browsing, etc.