It’s not clear what either set of numbers mean. The NSF lists some 5.5 million working scientists in the US alone, with 16 million additional people working in related fields. 128K means roughly a 2% usage rate. Should that be considered traction? How much of that 128K is from Google searches where the visitor was a non-scientist who immediately left the site? Perhaps a more meaningful analysis would be looking at growth in usage and membership over time. Many of these sites are 5 years old if not older, so one would think we’d be able to see if they’re really catching on.

Thoughts?

Also, a small correction about Mendeley – it does have a web interface, and their building social features which I’m already finding useful. More to come in that respect you can be sure.