I like Picasa much better than iPhoto. Why?
1. I tried to import a bunch of videos taken with my digicam to iPhoto. 1 of them is 1GB in size. Regardless of what I did, iPhoto choked on this 1 file. Everytime I connect my camera, it said "ready to import," and when I pressed import, it started importing, but in the end it didn't transfer the file at all. So I had to go back to my windows PC, imported the file, and copy the file manually to my Macbook.
2. Picasa has these nice effects such as glow and soft focus that you can customize. The effects in iPhoto are more limited and no customizations.
3. Picasa has a tray where I can "hold" my photos while I'm browsing, very useful for a large library. No such thing in iPhoto. I guess I can create an album, and drag-n-drop the photos, but the tray and hold feature in Picasa is much easier to use.
4. The Picasa Web album plug-in for iPhoto doesn't support uploading videos. :(
I just hope that Google and Apple will colaborate together to make either iPhoto better, or Picasa for Mac.