For such a historically sophisticated and innovative browser, I am baffled that it took the folks at Opera so long to implement extensions. With the advent of Firefox, extensions seem an absolutely necessity for a browser to be competitive. That said, Opera has always offered a relatively comprehensive out-of-the-box feature set, even sating some power users' needs.
Anyway, I digress. Opera 11 alpha is available for playing with, and I, for one, am impressed. When the extension 'market' becomes saturated, it may one-up Chrome. But only time will tell ...
http://www.opera.com/browser/next/Also: hot diggity, do I love the installer.