Mohan Kumar and Marco Conti organized an EU/NSF workshop on Future Directions in Pervasive Computing and Social Networking for Emerging Applications. They managed to get together an interesting set of people and the discussion in the break out session were very enjoyable and I got a number of ideas what really are the challenges to come.
There are the position statements on the web page and at some point the identified grand challenges will be available.
PS: blackboards are still highly effective 😉