Picasa Web Albums added some new features for managing your favorites and your fans. As you probably know, you can add any Picasa Web user as a favorite to get notified when he uploads new pictures. When you add him as a favorite user, you'll be included in his list of fans and he'll receive an email notification.
Until now, you couldn't remove users from the list of fans, but Google changed this: if the list of fans includes spammers, you can block them. Users "will be blocked from commenting on your photos and adding you as favorite. Blocking someone cannot be undone," mentions a warning. You can also block users who post offensive comments.
Picasa Web Albums added a list of "suggested favorites", which includes all your contacts that use Google's photo sharing service. It's a good opportunity to find interesting photos uploaded by your contacts and to add them to your favorites.
But if you can add users to a list of favorites, why is there no option to favorite images? Picasa Web added a link below each photo: "I like this" and the number of likes, but you can't keep track of the photos you like.