Seeking data on Yahoo! Groups and competitors

I’m curious to see if anyone has data on the biggest providers of online network services. According to my sources, they include:

Yahoo Groups-90m users
MySpace-100m users (and many thousands more in the last day or so, no doubt) users
Neopets-30m users
Facebook-7.7m users

Jeff Weiner, SVP of Yahoo Search and Marketplace, reported at Yahoo Analyst Day on May 17 that Yahoo Groups has 90 million members. Does anyone have any more detailed information on this number? Are these 90 million members receiving and reading their Yahoo Groups emails, regularly visiting the Yahoo Groups website, or doing anything else to prove that they are “active” members in some way? Or does 90 million simply refer to the number of users who at some point in the past registered with a Yahoo Group, but who are not necessarily participating or involved in the group in any way anymore?