"you can't buy something, tell everyone it's awesome in order to drive up the price, and then sell it"
I think you're missing the crucial aspect that the thing in question
must not actually be awesome. Since Bitcoin is, in fact, awesome, this doesn't seem to apply.
Seriously, though, I see early adopters "cashing out" in order to buy mining equipment and
mine more Bitcoins. And I seriously question whether anyone has sold Bitcoins in order to hold fiat currency.