Yeah... it's more of a "pump and dump" scam than a ponzi scheme.
I think of Bitcoin along the same line as penny stocks... something that is basically worthless, but can be easily inflated with some good story and enough suckers to buy into it.
Then you sell out of your position quickly, and watch the whole thing crash. If you're lucky, people will forget what what happened in a few months and then you can pull the same scam all over again.
Hell, Bitcoin has already crashed before once when Mt Gox got hacked in 2011. Do you really want to invest in a "currency" that can go from $30 to $1 in less than a day?