Ever since iLife '04 I've been using iPhoto to catalog my photos, and it's been doing a good job since. One of the much touted features of iLife '06 was that it could easily handle a library with over 200,000 seamlessley and true to the point I've found scrolling much more responsive.
Apple today released Aperture 1.1, the Universal Binary equivalent of the earlier version. I've found that UB versions are (naturally) much more quicker to startup and to run. Although up until now Aperture was in a price bracket far out of my reach (US$499) but with the 1.1 release there has also been a considerable drop in it's price, down to US$299.
So now that it's in a price range far more affordable I'll be keen to give it a go to see what improvements it has over iPhoto.