The "Web 2.0" mindset, at least the mindset I've seen most often on HN, is build it fast and get it out there to see if it has value. I also think there is some thought to how the solution can be monetized, but plans change in response to changing environments.
Current technology does make this valid in some sense - you can launch very cheaply and, if you attract enough interest, get bought by a larger company. As I understand this is YC's general approach. But it seems that Twitter tends to refuse buyout offers, so I they are more of a classic dot.com.
Sadly, this is not the Web 2.0 mindset. If it was things like Twitter and Facebook would have been "monetized" a few months after their launch, when it was abundantly clear that they offered value to people.
IIRC, that was supposed to be our lesson from the dot.com bubble :) The early hype about "Web 2.0" was that this time around we're doing it for cheap and with a revenue model...