The company valuations are based on the same thing though, potential for future revenues.The difference between this "Dot-com Bubble" and the last one is that, back then, the population of the Internet was comparatively tiny. Now, everyone is on the Internet.
Web services like Instagram can be worth hundreds of millions almost overnight simply because of the sheer number of quality visitors they get. Advertising.
Market analysts here in the US are saying the buyout bears the hallmarks of a bubble now and that Facebook won't make the money back.
The whole following people who aren't your (Facebook) friend to look at their photos thing? That's very niche along the lines of Myspace.