I broke down and bought Aperture the other day in the app store. At $80 it’s a lot cheaper than it used to be and I can load it on all my Macs.
I have over 20K photos in a couple of iPhoto libraries and I hate having to exit iPhoto to switch libraries. Granted Aperture isn’t a whole lot faster at switching libraries but you don’t have to close the app to do it.
So far I like it better than iPhoto.