The Opera/AJAX thread reminded me of something I've been greatly enjoying for the last few weeks and have failed to mention here.
While StumbleUpon's website works flawlessly with Opera, the devs at StumbleUpon have insisted it wasn't possible to bring StumbleUpon to the Opera community citing Opera technical shortcomings. I've disagreed, and limped along using a number of custom buttons I'd made that allowed me to do most of the core functions--rating, commenting, et cetera. More ambitiously, Kyle Anderson developed a custom menu/toolbar for Opera that effectively brings all of Stumbles features over to Opera seamlessly. Even better, in its menu form I find it far more keyboard friendly than the official StumbleUpon toolbar.
Opera Stumbler 
