Yeah, I was sitting there during the keynote thinking, "Why would they only import MPEG-4 video?" My hunch was that there was more to the picture than that.
So far, iPhoto 5 has handled any video generated by a digital still camera that I've tried to upload, including .avi. Whew! This is a big deal for me, because I've always wanted to store my camera videos along side my still pictures.
As for your photography habit... I'm afraid iPhoto 5 is just going to deepen your addiction. But you have lots of company here :)