I normally could care less about a new photo-site, but there is one feature that I'm just crazy about: distributed authentication.
See the screenshot from their login page (taken from the above review):
I think this is the second service I see the allows this kind of distributed authentication, the first being LiveJournal and their comment system. But Zooomr takes it to the new level, by using distributed authentication instead of providing a registration step.
You see a lot of people, specially the 37Signals guys, talking about the importance of doing simple registration procedures. This is the next step: no registration at all to start using the service.