Long time Opera user here. I just installed Opera for Mac on my new MB and am very, very happy that I can still surf in the same Opera environment.
There are lots of reasons I prefer Opera, speed has always been at the top of the list. I didn't realize, though, how much I appreciate the mouse gestures until I had to spend a week or so with Safari until I installed Opera for Mac, and I kept shaking my Mighty Mouse and nothing was happening. With Opera for Mac, you can shake your Mighty Mouse for all its worth.
I don't want to sound like an Opera fanboy here; I just want to point out that Opera for Mac is a good implementation of Opera on the Mac.