The single sign-on is an often heard request these days. Nearly as much as a dashboard, er central interface to monitor all one's friends across the various walled social gardens.
I have been watching ClaimID and Marc's People Aggregator to make huge strides on this front. Some recent conversations seem to point to others possibly providing this solution. So far it is the early adopters that are needing these tools, but a recent post by Scott Andrew about people moving from MySpace to Facebook makes me think the cross-garden social tools will have a mainstream appeal in the very near future. Well, those of us that are veterans of the on-line services of the early 90s will recognize the need as our friends jumped from one closed service to another when there was a 5 dollar a month fee hike. Your buddies left Prodigy and went where? AOL, Compuserve, Delphi, usenet groups, etc.?
The current web environment makes the keeping up with your friends (if they grant you permission - this really should be the case) easier across closed social services. Digital identity will be essential as will our trusted list (or grouped list) of friends we want to keep in they loop with our life (lives).