One of my interests is the Internet of people and Pocket Switched Networking (PSN). These opportunistic networks are created when personal mobile wireless devices such as smartphones are able to communicate with each other directly over short range wireless connections.
Opportunistic networking for inter-human communication is an ongoing research topic, and outstanding challenges include (but are not limited to) Peer Aware Communications (PAC) for neighbour discovery, security, addressing, and efficient data routing.
My research mostly focuses on opportunistic data routing using clusters. But here's a list of other projects which all have opportunistic data transfer between personal mobile wireless devices in common:
Please note that this is an ongoing effort, if I've missed anything then please let me know. If you're looking for investigations into Delay Tolerant Networking (DTN) there is a list on Wikipedia, and N4C made a very nice summary here.
Floating Content deserves a mention for no other reason than I like that particular problem, and see it as one application for the Internet of people and PSNs.