One of the things that finally swung it for me to get a Wii was the Mac App Wii Transfer. It’s not quite as slick as the Apple TV, but fits nicely with my fetish for using things for other things. The music application works really well, but movies need to be converted before they can be streamed, which can take a while.
Only recently did I have a poke around and realise that movies are converted to Flash Video (.flv) and stored in /Library/Caches/Wii Transfer/Converted Movies/ folder. Using a handy bookmarklet I can now save YouTube videos directly to this folder and have them immediately available in Wii Transfer.