Here’s an article with an overview of online products out there for research social networking; the big gap in the article is that no institutional products are included such as Profiles, VIVO, etc. This is noted in one of the comments at the end, by Titus Schleyer.
That aside, there are interesting opinions in this piece, a few clipped below, and perhaps pointing to the current status of the space, where the sweet spot has not yet been found.
“After six years of running Zotero, it’s not clear that there is a whole lot of social value to academic social networks,” says Sean Takats, the site’s director, who is an assistant professor of history at George Mason University. “Everyone uses Twitter, which is an easy way to pop up on other people’s radar screens without having to formally join a network.”
Scholars aren’t interested in sharing original ideas on such sites, [Christopher Blanchard, an adjunct professor of community and regional planning at Boise State University] now believes, “because they’re afraid they’ll be ripped off” and because they simply don’t have the time.
“We have thousands of new discussions taking place every day—scientists helping scientists without getting anything for it,” [Dr. Madisch, of ResearchGate] says. “Three years ago, people were smiling at me and saying that scientists aren’t social. They won’t share information. They were wrong.”