Gary George has provided an interesting and in depth article at VMS3.info that analyzes a wide variety of social networking solutions using Mitchell Levy's Industry Analysis Value Framework Template. I hadn't -- prior to looking at the article -- known anything about Levy's Value Framework, but it seems to lead to a relatively sensible segmentation of many of the social networking offerings, including Classmates, Ryze, LinkedIn, Ecademy, Friendster, Friendzy, Huminity, Spoke, and LinkSV.

Scott Allen provides a detailed review of the article, where I got the pointer originally.