LinkedIn (SAI 25 #8) may have been trampled by the likes of Facebook (SAI 25 #1) and MySpace in terms of users, but at least it can sell advertising. Kevin Eyres, LinkedIn's managing director for Europe, told IDG the social network for careerists is earning $75 CPMs (cost paid per thousand viewers) for advertising in the US and $50 CPMs in the U.K. Prime reason: the site's average user is 41 and makes $110,000.

Since LinkedIn knows the professional histories of its users, and can target sales execs, c-level managers, or certain industries, we can imagine high ad rates for advertisers looking for a business niche. Still, we have a hard time believing this is an average CPM for LInkedIn. But we don't have a hard time believing that LinkedIn's average CPM crushes that of Facebook, MySpace and other social networks who routinely struggle to get CPMS above a buck.

Facebook (70 million) and MySpace (200 million) have an enormous scale advantage over LinkedIn (17 million); Facebook in particular is encroaching on its user base. But if LinkedIn can profitably establish its niche of working professionals, which advertisers covet, they have a franchise.