I am super interested in this, and I think it is a fantastic idea. One critical problem (for me): I don't use Facebook. I look forward to seeing the address book integration, or even better, G+.
You can use the address book too! No Facebook required.
I could have sworn I saw that address book integration was upcoming (not available now). My mistake! Thanks for the heads up. That said, G+ sign in would still be cool. :)