With release 3.5 the free Google Picasa photo manager and editor app is now cross-platform (Intel only on Mac):
... we launched Picasa for Mac as a beta Labs product 9 months ago. Now that Picasa for Mac has almost all the same features as the PC version, we've decided it's time to remove the beta label. Remember that Picasa for Mac is designed to 'play nice' with iPhoto -- Picasa takes a special read-only approach to editing photos stored in the iPhoto library, duplicating files as needed, so your iPhoto library isn't ever affected when you use Picasa.The appeal of Picasa 3.5 for iPhoto users is the tight integration with Picasa web albums, esp. with "Faces" and geotagging.