How big is the internet?

I heard about the Map Your Name "game" from Ton Zijlstra.  A group of Portuguese students think they can find out the "exact number" of internet users within a month via a viral campaign.  They've gotten about 4,000 people in six days - a whopping six in the Chicago area. 

But, have a go, I already did.  The link takes you to "my" page, and if you sign up from there, I get some kind of credit for spreading the word.  (And to Ton - I didn't click on the right link, so you are missing some credit.  Sorry.)