Unimpressive! How, except for the eye-"candy", is this different from having a separate firefox window open for each different category of web-pages? I just think it consumes more time having to click the TabCandy button, look for your web-page from the confusing layout and clicking on it to open it. I have an extended tab-bar of about 3-4 horizontal bars and it's really easy to navigate through the tabs if you have them all at one place(atleast for me it is).
FIrefox is a memory hog as it is and with like .. 50 tabs open at a time within just one window with graphic-supported navigation, I can foresee some frustration!
Also, the person in the video says that when he open the links from a page, they land up at the end of the tab stack making it difficult to navigate. This is incorrect for the version later than 3.0(I guess) for the firefox browser.