What makes them different/better than adsense? As far as I can tell, they're the same with some barriers to entry like minimum page impressions etc. Now if they did ads in SERPs, I'd say they may have a USP. And since they don't appear to be an SE themselves, they may be well positioned to do so. I've always thought google doesn't support adsense in SERPs because they think they'd be funding their competition.
Fastclick will be interesting to watch this year. They don't have many employees for their size. They're profitable, raised $75M in a round last year and will raise $90M in this IPO. That makes the iprospect & infosearch deals look tiny. Fastclick is loaded with cash so it will be interesting to see what they do with it. Fastclick needs to do more than just arbitrage impressions.
fastclick is the leader in the segment of ad networks they are in ... they have a good rep for paying publishers on time and for paying at levels that are as good or nearly as good as their compeititors such as casale and burst media
this kind of ad network usually serves banner ads and not text ads on cpm basis
i think they will do very very well, especially in the short term ... who can say with any certainty about 2 to 5 years out ... we could guess ... and that guess might be a nod towards fastclick ... but when you go that far out ... there are a lot of variables in all things tech related