The big problem with Groupon, even compared to social networks, is that there's no network effect to help entrench their position.

Consumers might use a Groupon coupon today, a LivingSocial one tomorrow, and a Facebook one next week. There's no significant motivation for consumer loyalty.

I like Groupon too, but the Burlington Northern is going to be a significant player in freight shipping 50 years from now with a high degree of certainty. How sure are you about Groupon?

I definitely don't think they deserve the valuations they are receiving. I just think that they are much more worthy of being a public company than either Facebook or LinkedIn are. People are always going to want to save money, that demand isn't going away. People change social networking services like shoes.

I felt the same way about Facebook until I read Spolsky's "every time they figure out how to make 10 cents from their customers they get to fill swimming pools with money" comment. Facebook has also become defensible, in a way that almost provides an argument against Buffett: it's not a question of "which social network will take all the chips" (let me answer that for you: Facebook), but whether the social space is going to have a large value.