One thing nobody has mentioned is that MySpace.com, Facebook.com and YouTube.com were weak domains prior to becoming social networking megabrands. This suggests you don't need a premium generic name to succeed in this field.
If generic names are so valuable, how come Amazon isn't called Books.com, eBay isn't called Auction.com, and Google isn't called SearchEngine.com? All 3 could have bought their generic equivalents and switched to them.
Presumablly they didn't because brand is infinitely more valuable than name. The value of blockbuster generic .coms differ according to the nature and structure of the industry they operate in.
For example, if an industry is fragmented, ie it has alot of small players, but as a whole is worth billions and each customer is very valuable, the obvious generic .com is worth a fortune because you can sweep up alot of confused direct navigation traffic and people looking to make sense out of the breadth of choice available.
The domain Debt.com would fall into this category. The debt consolidation industry is worth a bomb because so many people are in debt but there are 1000's of advisers desparate to switch you to another loan for a few hundred bucks commission. Here, having the obvious generic domain could give you a massive branding advantage amid a throng of different players and the value of the domain itself would add to your credibility. Hence, I would value Debt.com at $5m-$10m.
I see Social.com at completely the opposite end of the spectrum and value it at $300k-$500k. Online social networking is dominated by YouTube, Facebook, and MySpace. The bigger your registered member base the more watercooler and dinner party mentions you'll get and the more people will register, so sites grow by a snowball effect. Word of mouth is more important than generic domain credibility, search engine rankings and PPC traffic.
I don't think it would make commercial sense for YouTube or MySpace to buy Social.com to capture a few thousand extra hits. If anything, that would dilute their brand, not enhance it. Less confusion and fragmentation exists than in other industries, you can't just wave your blockbuster generic domain and herd people to your site. The laggards joining Facebook, MySpace, and YouTube do so because they are sick of hearing about it from friends and TV and want to know what all the fuss is about. Other laggards are not going to have a social networking epithany experience because somebody buys Social.com and develops it.
Another critical factor, is an extra customer isn't worth much for Facebook, MySpace, or YouTube. You need tens of millions to make these concepts work but once you get there, the marginal revenue from an extra member diminishes. Again, this is different to an industry like Debt consolidation, where you can run a very profitable small to medium sized business on a thousand customers per year. If you buy Debt.com and it wins you another 5,000 debt consolidation customers per year, it will pay for itself within 5-10 years.
Anybody starting a social networking site would have a major problem competing against the giant snowballs already in the market, and realistically, as long as the current fad lasts, it's these guys who are going to be in pole position whatever domain somebody else comes up with.
I say as long as the fad lasts, because in the early to mid 1990s when I should have been registering domains, I spent most of my Internet time on chat sites and within the tiny microcosm of people with Internet access at the time they were as popular as as social networking sites are today. I looked up Chat.com and it seems that Download.com use it to forward people to their list of free to download chat and messenger software. That seems like a pretty unglamorous end for what would have been considered Social.com's equal back then if anybody had realised how valuable domains would turn out.
If you want to start a social networking site it makes more economic sense to register RedCarrot.com or the equivalent and spend $1m on programming. If the concept is original enough you'll get far more commercial benefit than spending $1m on a domain.