How many Web services can one person use?

A post on the NY Times Bits blog points out that there are only so many social networking services any one person can keep up with on any given day.  I know this is certainly true in my case.  I’m always talking to clients about the relative importance of Web 2.0 and social networking tools to their higher-education concerns, but the fact is that I can barely keep our own blog updated, let alone check in on my Facebook page or remember to post chatty musings to Twitter.

Who are these people who maintain accounts with Tumblr, Stumbleupon, LinkedIn, Mixxd, and CrowdVine— what do they do all day?  How do they get any work done?  

(OK, I made up Mixxd. But I think the others are real.)

Update: Tony from CrowdVine comments that CV’s network is transient— used primarily during conferences for attendees to let each other know which sessions are “hot.”  That’s a good point— it’s easy to understand how transient, explicitly function-oriented tools can be useful, and if CrowdVine’s efforts really are directed at serving temporary social networks like conferences, I wish them well.  It’s a good idea.