There will be losers in the big game of bitcoin speculation.
And those losers will eventually sue the winners.

Thus, the debate about bitcoin being a Ponzi scheme or not is probably only going to be settled once we've had at least someone file an according lawsuit.

I mean to say, IMHO it is absolutely irrelevant whether or not bitcoin actually is a Ponzi scheme. What finally matters will be the decision of a few grumpy old men in judges' gowns.