You can't say before the IPO that the company is worth 75 B or 100B and then after the fact say it's their fault for investing at those valuations. That destroys the integrity of the silicon valley investment environment.
There is now some rethinking of that assumption as more financial information from these brands is made public.
But if some analysts are pumping Facebook and no one from the silicon valley is trying to temper expectations, people assume that the valley believes the same valuation numbers. The result is long-term damage to the credibility of SV and a contraction of the investment supply. After all, if someone comes up next year and describes DuckDuckGo as a $100B company, why would anyone believe the valuation? Everyone would point to Facebook and give it a much lower valuation even if it probably deserves a much higher one.
To make it clear, I think that this type of chicanery from wall street is scorned yet expected in the eyes of most people. We have all accepted the fact that they will pump stocks, especially at the top (http://www.scribd.com/doc/86194691/Long-Good-Buy was Goldman's paper which essentially gave a bullish case for equities at the top). But there is still some credibility lent to silicon valley, which people should not squander in the interest of one investment.