Today, PlayStationLifestyle (linked above) has revealed that SCEA has indeed registered PlayStationCloud.com, as follows:
SCEA San Diego Studio
10075 Barnes Canyon Rd
San Diego, CA 92121
SCEA San Diego recently mentioned while speaking to Gamasutra that they would be exclusively working on PSN game development. This goes against all speculation so far pegging PlayStation Cloud as a social networking service. Of course Sony San Diego could very well be developing a service or application, for the PSN with PlayStation Cloud.
Whatever PS Cloud is, it seems as though it's going to be coming from Sony's San Diego Studio.
If PS Cloud is a realtime mini-facebook for psn users, it would be huge. There would be a real niche for it. Id love to be able to see when my friend are unlocking trophies etc. It would create a great community experience.
Of course, it could be something completely different. My bets are it's a tie in with the xmb and home, like an update feed, that will tell you when one of your friends logs into home/playing bowling/unlocking a trophy etc and their update status, possible in game screenshots for others to see, facebook-style profiles . I'm only going on whats rumoured though.