I was excited about the iPhoto demo at Steve's keynote. But before I wrote about the app, I wanted to have my ducks in a row testing-wise. Not everything I was told from various people proved accurate when I tried it myself. Still, not too bad on the timing of the article, eh?
As for the Canon G3, I don't have a .crw file I can test. But I did have one from a Canon G2, and iPhoto 5 would not accept it. I opened it in Camera RAW just to be sure. And yes, Photoshop Elements 3 could read it. So, I would say you might be out of luck with the .crw from the Canon G3, but I'm not sure...