Since I switched to Mac a few years ago I’ve never felt the need to venture too far in to other photo library managers as iPhoto from Apple, which comes with every new Mac, seemed to be all I need. It even has intigration with Googles Picasa online which is my prefered online photo manager.
But with iPhoto you are tied to the Mac and upgrades cost. Picasa is cross platform and free but the main feature that cought my eye was the face recognition.
Nothing new with face recognition but they way Picasa dose it makes it a joy and fun expieience to work with. Such is the ease of this feature that I was able to tag over 5,000 faces from around 2,000 pictures in a matter of hours.