I like Tab Effect, but I wouldn't go so far as to say it's useful. It's an extension for Firefox that adds a sort of rotating cube effect when you switch tabs. It's powered by DirectX 8, so it'll only work on Windows, and how well it performs may depend upon the quality of your graphics card. My graphics card, for example, is a piece of crap, which may be why Tab Effect performs a tad sluggishly. There's a slight delay after clicking on a tab and when the effect kicks in, and the rotation is a slower than I'd like.Like I said, I'm not sure how useful Tab Effect is, but it's definitely a cool concept. We've seen this sort of effect with desktop-switching before, so tab-switching is a natural progression, but as it stands it's pretty limited. But it's only 1.0, so maybe after a few revisions it'll be mind-blowingly speedy, intuitive, and useful.
In today's day and age of multiple viable browsers, it
can be a minor annoyance to have to copy and paste URLs from one browser window to another to move a page from, say,
Opera to Firefox. Or IE to Netcaptor. Or Maxthon to Firefox. You get the picture. 
