How many social networking sites can we truly use?

A point Jon Udell made the the MIT Forum has rattled in my head for the past few weeks. He talked about "Social Media Fatigue" to which an audience member responded that he believes people have a tolerance for memberships in about 5 social networking sites.

Since each one requires a username and password, I can understand that. I mean, how many different sites can a person really join and become an active participant in?

So now what? The technology is interesting and the benefits pretty awesome, but a community is only as good as its members. Enter Yahoo (and Google). Your Flickr ID is now a Yahoo ID. Your Blogger ID is now your Gmail address. In other words, by using just two IDs you get a lot of access. You have access to Yahoo Groups, Google Groups, Blogger, Yahoo 360, Flickr, YouTube and who knows what else that comes down the pike. So, what's next? Well, why not start selling access to the community? In a sense, create a federated identity process. Yes, these groups will still need to gather their own data and information, but once someone is logged into Yahoo or Gmail they should also be logged into your site.

Of course, there is also OpenID, something that Simon Wilson has been writing and speaking about.

Yes, I know browsers store a lot of this information so no, I don't need to log into the New York Times, Boston Globe and Tabblo (client) each time I visit, but what is something happens to my browser? What if I'm using another browser at a friend's house? or maybe I'm accessing from some other site? How many IDs should I be expected to remember?

And yes, I know life will be better once we all have digital signatures on smart card chips that we can access through our local computers, but the day we have those never seems to come, so we can't plan on having those in the short-term. For now, it seems, just about everyone has either a Yahoo ID or Gmail address, so we may as well accept it, use it and just be happy.

Then we can join more than 5 social networking groups. Well, in theory anyway. Even if I am a member, how active can I truly be? Can I take part on a regular basis? How much participation is enough to be a member of the community? I don't think I've bought something on eBay in quite a while, but I have been running regular searches and may have bid on a few things. How much participation is enough?