The number I cited was their claimed active users.

I'm not sure why you consider $29 per human user a steal. There are two sides to a transaction--what you pay and what you get for it. What exactly do you think investors are getting for their money here?

Just compared to other industry metrics.

That's exactly why we're in a bubble. "Because other people are paying even more" is a really bad reason to pay too much for something. But that's the entire basis of Twitter's price--it's people investing in Twitter because other people are investing in Twitter (and other such companies) with no concern for whether that investment will ever return a profit.

So you pulled it out of thin air?

No. Look at the citations others have made within this thread. A rule of thumb is generally anywhere from $50 to $200 per head for social network type applications. See also: Facebook, MySpace, Instagram, etc.