This is even cooler than the faux-3D images that Picture Cloud makes: Photo site Zooomr has a new feature (went live this morning) that lets you put portals into photos. Portals are clickable zones that link photos together. For example, if there's a picture of a house, you can make the door into a Zooomr portal and link it to a picture of the inside of the house.
Here's a quick demo using CNET's headquarters. (Roll your mouse over the image to activate the portals.) You can zoom from the plaza outside the building, up our grand staircase, and through a door to the fifth-floor atrium. And here's the official Zooomr video of the new feature.
Lead developer Kristopher Tate told me he sees the feature as part Myst, part Microsoft Photosynth. Really it's more like the hot zones feature in QuickTime VR; or online, a much better implementation of Flickr's notes feature. No matter what you compare it to, it's incredibly cool and very interesting.
Since Zooomr already makes it easy to geo-tag photos, it should be easy to find images to make complex collections of portalized photos, for example, of popular tourist attractions. This feature could enable a very rich form of social photo linking. However, since portals also have the potential for abuse, there are restrictions. For the moment, you can create portals (on your own or others' images) that link only to your own photos. It would make sense if Zooomr let you at least link your own photos to other images on the service, and I expect this restriction will eventually be lifted.
Even without any group or social features, the portal feature will be a lot of fun for individuals and useful in many commercial applications, especially real estate.