Lately, I've been looking at the data emerging from social tagging services in the academic domain, particularly Citeulike, Connotea, and Bibsonomy. Here is how these three services look in terms of number of unique visitors per month for the past year.
At which point, they seem either a) pitifully insignificant or b) primed with the opportunity for dramatic growth.. If even a small fraction of the people that visit NCBI started to use these kinds of services, the data they could generate (e.g. simply metadata in the form of tags added to scientifically relevant things) is massive.