Tim, no sweat, it's definitely not a unique idea. As Greg mentioned, he did the same thing last year. I didn't get the idea here or I'd have mentioned it, sorry Greg
For those wondering how long it took me, well it really only took 4 or 5 hours to process when I used reduced size images, but we're going to print it big, so I had to redo it with the full size and it took forever on my cheap mac mini.
Also, after looking at Tim's image, I have to say it looks like AndreaMosaic cheats! But I love it - I was looking for that feature. The one I used just puts the pieces together as best it can. But I think AndreaMosaic goes a step further and tints the images to make the overall image really stand out. Right? Maybe I'll have to reboot to windows and make this over again.
Also, for those who'd like to use this image as a background or something, you're welcome to use it for personal use only (not for publication or websites), but I cannot provide a larger copy for various reasons.