they both have a certain feel to them. call it web 2.0 web 3.0 :) or just look at the graphics or the language and yes sometimes features too. "Share the love" / "concert-savvy friend" just an example. There are other bits and pieces too. You could say that this is the general trend, what attracts yc, and so on. of course. that would be the value of their vision. I don't have any arguments about that at all. And it's a good think that they can see it. but my argument is that this is the theme of yc.

Another thing I've noticed is how features that have been around for a long time (web time), are slightly "modified" (most times more simplified, either for the good reason of simplification, or simply because of lack of technical experience, or in the worst case because of bad copying) many examples of this. but since you brought up dropbox, the first thing brings to my mind is box.net. again I'm not saying anything bad about it. I'm sure its better since I know about box.net and their not that great anyway. but my point is that there are not that many selections that are either new innovative products or an old idea that you could say wow this is how it should be implemented. say Google for example. And, they have common theme to them. no not from the perspective of the consumer or what the products are.

I really don't know about how yc views things but the theme of yc is clear. alteast to some degree. either because that's simply the result of their total work and it just produces this, or intention by design to move in this direction or both.

if you go to many vc's site and look under their portfolio many times you can find a common theme in their select.

common theme is "build something people want". i guess you could call that a common philosophy as well.