The YouTube search and playback on WiiMC is awesome. Obviously there’s lots of video sites out there that people would like to have similar WiiMC capabilities for, but if any were to be considered for a future upgrade, I’d like to suggest http://www.justin.tv
I find justin.tv especially good for watching live (and previously recorded) sports from around the world that I’d otherwise never get to see, because they’re not shown locally.
I believe one of the problems getting it to work on video game systems previously was the fact that it used Flash 10, but apparently there’s an iPhone app for JTV so I think there’s a way, like YouTube, to get it to work.