I normally use iPhoto to organize my pictures but it has a lot of annoying limitations I'm just not motivated to sort out. So when a friend suggested Picasa, I figured I'd take it for a spin. After just an hour or so of fiddling with it, I found a couple of surprisingly useful features:
Sorting by color! This is fantastic for me as I'm constantly digging through my portfolio for different color combinations. The screen shot above shows a search for the color red in one of my folders. The files here are all jpegs or tiffs.
Face recognition. It's amazing and a little creepy how easily Picasa will troll through your photos and learn the faces of everyone you know. Next time you need to find a someone's pic for a birthday party, just click on their name and scroll through to find the best shot.
I should reiterate that I haven't tried that hard to work out the kinks with iPhoto but so far Picasa's sorting tools far outstrip anything I've seen in iPhoto. I look forward to seeing what else it can do!