It's funny, but as a pyramid scheme it kinda sucks. When the pyramid crumbles, everybody's left with a bunch of worthless bitcoins. At least in a ponzie scheme, the people at the top profit. A lot.
But if you've been mining bitcoins since the beginning, you probably have a lot. Now mining is no longer very profitable because more people are in on it; thus, it makes sense for the early adopters to convert their bitcoins to USD at Mt Gox. They make a load of money from the late adopters, and the late adopters are left with loads of worthless bitcoins (because eventually nobody wants them and you can't sell them). Sounds more like an MLM scheme.
This could be part of the scheme, however. This is a late phase of the scheme in which the early adopters are now fully stocked up on bitcoin, and are now hyping it very successfully. Late adopters want in, but the early adopters are not selling, and the miners aren't generating much anymore. Thus, supply is severely limited and the rate skyrockets, up more than 200,000% at this point. There is no telling what heights it will reach, but it's not over yet. At some point, the early adopters will start dumping, thus completing the scheme and leaving the late adopters with absolutely nothing.
I don't believe bitcoin is an evil planned-out scheme like this, but human nature may trigger this bubble effect.
