I just 'tested' the Autofocus theme and it doesn't really display images in their original format in a thumbnail, rather it cuts/slices them into what appears to be a pre formatted size? Not sure why but the 'try' view didn't display my images correctly.
I do see what you mean though by using the Tiled Mosaic function for a gallery. I hadn't thought about that. I suppose I could create a very large gallery using that format and make a static front page. That's something I think I'm definitely going to play around with. Thanks so much for the idea!