tedster - 5:03 pm on Jan 2, 2011 (gmt 0)
I mostly use tab stacking during research. I stack the tabs related to one task and they're all in one spot while I go off on another task. Then hovering on a stack's tab shows me a preview of all the pages in that stack which helps a lot.
What would make this a more useful feature for me would be a way to label a stack. Then one look at the toolbar label would tell me why I built that particular stack. That sounds like a pretty complex UI to develop, however, so I'm not holding my breath.