I have nothing against someone who knows how to make money & diversify his/her portfolio, but when someone talks nonsense its worth pointing that out to them.
The term "pyramid scheme" is charged, and often equated with "Ponzi scheme".
At least as an investment, Bitcoin is a pyramid scheme (though not a Ponzi scheme), in the sense that the earlier you got in, the more your investment will be worth, and without new blood entering, your investment doesn't grow.
The big difference to the usual pyramid schemes though is that in our case, it is just the bootstrapping phase of a peer to peer currency/store of wealth. In other words: it has to be a pyramid scheme, because it needs to start from nothing, and aims to grow to capture a huge market.
Lets say an very early adopter has paid lots of money for his mining equipment and bills but has chosen not to sell any of his bitcoins. If tomorrow bitcoin price collapses he will have a worse faith than someone who joined a year later than him but sold his bitcoins. Therefore In order to call it a pyramid scheme those early adopters should
1. make a financial gain bigger than the adopters that joined after him
and
2. have a GUARANTEED PROFIT from the fact that others joined later. In our early adopter case neither is true. This could be the case with many bitcoiners which haven't yet recovered their investment which they made into mining while others who traded on the exchanges but joined later than them made much more money.
Bitcoin is not a pyramid scheme because
3. there's not a level of differentiation between joining dates of participants, only that you acquire more knowledge of the inner workings of Bitcoin.
also
4. you don't have to make a payment to join, you can merely offer your services in return for bitcoins and doesn't require you to buy or mine them, hence no initial payment is required for you to join. Overstock for example keeps 10% of bitcoins for their products. They haven't investment anything into bitcoin but still they can interact with some of the earliest adopters without Bitcoin making any distinctions between them.