Google Adsense is way to monetize for many websites and blogs. But the revenues out of google adsense many times are too low as they are mostly CPC (cost per click) based. Dusty Reagan, a twitter application developer who built friendorfollow, soon realised that google adsense is not bringing enough revenues to even pay for the server, so he came up with featuredusers.com, which he first used for just his application, but as the advertizing inventory grew he opened it up for other twitter applcations as well.
Featured Users works on CPM (cost for 1k impressions) model. Users will have to pay 10$ for 1k impressions. Basically impression will have a link to user's twitter profile. Users who want to increase their followers see featuredusers as better alternative to Adsense as they will be advertizing on Twitter Apps which is very contextual as people using twitter application are already twitter users and follow for them is just a click away.
Try out FeaturedUsers and let us know the feedback. We will try to bring the Founder on TechI soon.