I really only use it for the post-it notes gadget. I genuinely find that gadget useful. It doesn't take up screen real-estate at all, since it's not always on top.
I'd use it for more, if there was anything useful for it. Pretty much the majority of what I find on Microsoft's site is internet radio players for every radio station known to man.
I took a shot at writing some stuff for it, but writing applications in javascript and html is god-awful, and not being able to debug anything using VWD Express pretty much kills the deal.
What I'm looking for, gadget wise, though, is a Windows Media Center remote that uses Sideshow, allowing me to browse an EPG gadget, a gadget showing me my recordings, and a gadget allowing me to set a recording. That would be pretty neat to do all on the remote, without having to wake up WMC.