I accidentally ended up in the comments of Chris Dixon's post on this and produced this giant wall of text that basically sums up my problem with all those arguing that a bubble couldn't possibly be happening, so, I will copy pasta it here because, as I said there, THIS.
I'm just having a hard time with this argument - I don't think he (or anyone else I've seen) is arguing about large, established companies. Some people are questionable about the later-stage *startups* (different from *established companies*), but I think there has been consistent concern about the issues in early stage startups. We are spending a lot of time comparing this bubble to 1999, but I'm pretty certain that they are not similar in any way. The comparison between the two is useful and accurate in the same way that say, the Great Depression is useful for understanding the Great Recession. Which is to say, in limited, critical doses. Furthermore, a bubble is one of those things that is ridiculously hard to prove the existence of during it's growth period. The entire point is that we won't see failures until we see them start happening at an alarming rate. I suspect that if we see that occur here, it won't be companies that are failing spectacularly, but investors.
Again, all these points are related: bubbles happen most frequently when the value of the goods is not clearly discernable. This is a period of uncertainty - no one really knows how the social internet will play out, just like no one knew how big search or e-commerce would be in the 90's. Now these quantities are a bit more known, so it's harder for these companies' values to inflate as much. chris dixon raises the point in this thread that startups are now being seen as a viable career path, and I suspect that these things are fairly related. However, it makes a certain amount of sense that during a bubble, accompanying the over investment of monetary capital into a space is the over investment of human capital into the space. My concern is that being geared towards a career in *startups* is as worrisome as a career in *finance.* Both do certain crucial things, but more important than either of these things is a commitment to certain types of work. I am far more interested in a generation of people that have educated themselves to create, build and innovate - whatever institutional vehicle that facilitates it best for the skills that they acquire. Still, as painful as bubbles and bubble bursts can be, they're crucial to innovation - the cyclical nature of Silicon Valley is that they take on industries with high uncertainties, whose value is as of yet undetermined. And it takes that exploration to determine what works, and what those values are - I compare it to the periods of boom and bust in evolution, that result in diversity and efficiency in turn. (I once tried to write an ill-fated college paper on this).