Podtech's LunchMeet vidcast has done an interview with Kris Tate and Thomas Hawk of Flickr rival Zooomr. Zooomr has a lot of nice features, but one thing that stood out in the demo was the use of popup icons that appear when you hover over the photo. As you hover, they show up in the corner, and allow you to do things like open the photo up as a lightbox or toggle its "Fave" status (i.e. declare it as one your favorite pics).
The neat thing about this popup mechanism is that it's pretty consistent across the site...whether you're looking at thumbnails or a detailed view of the pic, you get that consistent set of icons. This means you can mark a pic as your favorite without having to open it up first. In the ongoing effort to build a rich collection of tags, it's also conceivable that users could tag the photo with a similar popup mechanism.
From an eye candy perspective, the Ajax-powered (or DHTML if you like) portal feature is pretty sweet too. Like Flickr's popup notes, the pic shows a box outline. With portals though, what you see when you hover over it is a new inset photo and you can actually scroll around the second photo while looking at the portal photo. And of course, clicking on the inset photo opens it up. Hard to explain, but easy to understand if you try it out.
Watch Lunchmeet's Eddy and Irene talk to Zooomr's Kris (founder/CTO) and Thomas (CEO) ...