I'm forever forgetting the differences in specs between PS3, Xbox360 and Wii. I've been meaning to write a comparison for a while, but thankfully found someone else has written one.
A couple of the most fun parts of the comparison are the CPU and Memory. Wii has about 1/8 of the memory of the other plats, and the Wii has a single core which is less than 1 GHz (as opposed to 6+ cores at 3.2 GHz). I still want a Wii mind you.