The new user interface has a very Lightbox feel to it with nicely placed 'Like' and 'Tag' buttons when the image is rolled over. It breaks away from the more traditional vertical layout that many websites use to place comments on the right, perhaps in a bid to focus users to spend more time considering the social interaction around a photo rather than the photo itself.
Controversially, the new comments-on-side interface allows a large blank space for advertising on photos. This will inevitably add a very large new revenue stream, especially given the amount of time the average Facebook user spends browsing photos on the Social Networking site.
ComScore and BuddyMedia recently put together this excellent report on social media which included the following chart which makes it pretty clear why Facebook is keen to run as many adverts as possible on users photos.
Since it's recent IPO many are speculating that Facebook may make some unpopular commercial changes in order to boost income which may cause it to go the same way as MySpace.
Of course it is only a matter of time before this change is rolled out to all of Facebook and the people cry out in revolt as they do at every change. Give it one week and people will probably no longer notice but I'll bet this change will pay off significantly in terms of new revenues.