I think we are in a bubble in the sense that none of this family of companies (facebook, zynga, groupon, twitter) increases the overall productivity of society as a whole (or even their user base for that matter) and yet still garnering such high valuations. Whereas if you look at the last generation of tech companies (especially google) did in fact increase the productivity of the overall society.

I think the overall emphasis on marketing is an outcome of commoditization of software. In an earlier hn news item, OReilly talked about the thing that is adjacent to whatever is commoditized becomes valuable. I think in the case of software commoditization, that adjacency is data. User data has become much more valuable because it is now the biggest moat that can protect a tech business. Its no longer the software and hardware The more ability you have to collect and monitize the data, the more defensible your business becomes. The only way to collect more user data is to have an effective funnel driven by marketing.

Thats my 2 cents anyway.