And this is how you can tell it really is a bubble: people talking about becoming billionaires. It's silly and smacks of a get-rich-quick scheme.
If a bubble is best defined as irrational exuberance taking valuations as multiples of intrinsic value, then the fact that the exit strategies are different and there are fewer IPO's than 10 years ago is irrelevent. Web 2.0 seems to be clearly Dot Com Bubble 2.0.