The developer/publisher spaces idea has a tonne of potential when you think about it. I didn't really think to much of it initially, but thinking about it, it could be quite powerful.
It was being discussed on GAF, but it would be very neat if a developer can host online tournaments in their games from a themed dedicated space, with displays around you potentially streaming video from the games people were playing, or perhaps if it was possible, live video. Imagine in a tournament, people launching into, say, races from this dedicated space, watching them race live on a big screen, and then having them return back to the space afterwards to congratulations (or comiserations) from the rest of the people participating there.
Another thing I was thinking about..consider if the ESA (organisers of E3) created a themed E3 space where people could gather and, perhaps, watch live streams of conferences or the like. These kinds of events are very 'social' in a kind of weird way already for people online..people go on to messageboards and post furiously during them. So to be able to share that experience within a closed console community would be very cool. Ditto, media outlets could create spaces to pipe their coverage too. Harrison mentioned during the demo that partners can put html on displays, so if that can be HTML hosted elsewhere, it could be pretty easy for a 1up or IGN to integrate their existing set ups with that. So, for example, you could go and keep tabs of a Eurogamer live blog of an event on a big screen in their space. Now, you might wonder why do this if you can just go online on your PC and watch the live-blog, but again, I think people are already inclined toward sharing those events, and it would be cool to be able to do that in a console community. Something like home could facilitate that perfectly.
Of course, these are all "coulds and woulds" right now, mere possibilities. But I guess just the more I think about it, the more potential I see there.