I just tried Groupy and I must say it's a nice idea. I've always been looking for a way to better handle my multiple Explorer windows.
I'm sure I'm not the only one who hates how Windows groups things on the task bar, and thus has it turned off. I would, however, like if I had the option to make windows in a groupy disappear from the taskbar, to be replaced with an entry for the groupy itself. This would allow me to potentially have two groupies (this is starting to sound weird...) of four Explorer windows each show up as two taskbar tabs, rather than either eight or one.
It would also be nice if my Explorer groupies would persist through a reboot, but I'm not sure how you'd do that (or if it isn't already implemented).