I recently installed the latest MSN toolbar with support tabbed browsing. Having never used a browser with tabs, I'm finding the experience... well, frankly not up to the hype - It's nice, but I can alt-tab just as quick as I can ctrl-tab (plus alt-tabs allow me to flip between windows, rather than simply cycle through them).
Anyway, that's not the point of this post. One thing I've noticed is the rather glaring flashes that happen when switching between tabs. It appears that their implementation of tabs basically consists of hiding the various IE windows and switching which one is visible when you change tabs. This means that switching tabs can be quite annoying visually and can sometimes take longer than switching windows using alt-tab).
For the moment I'll keep using them for the sole purpose that you can be reading one page while keeping track of whether another page has finished loading or not. Other than that I'm not convinced...