Where is my cloud addressbook?
ganley: I've looked pretty hard into this, and the prevailing opinion seemed to be that the trouble isn't technical, it's social. Do you really want your friends putting your contact info in the cloud? In order for this to work, you really need a mechanism for people to approve sharing their info, control what gets exposed, etc. If you built such a mechanism, it has some obvious advantages - e.g. someone can update their own address and have the change be automatically propagated - but it also makes it much more complicated. It's doable, but established social sites (Facebook, LinkedIn, Google, etc.) have such a head start that you'd have to worry about them stomping you from day one.