You can easily do it in an hour or two by copying and pasting some code off the ethereum site.
They encourage it. I like to think of ethereum as a ponzi scheme which spawns ponzi schemes (some of which themselves are intending to be a new platform for generating currencies...)
Not every questionable, bad or even fraudulent financial construct is a Ponzi scheme. Unless a coin has a clear promise of payout that the people organizing it would have to satisfy, it can't be a Ponzi scheme.
The main method is to create a cryptocurrency using Ethereum's ERC20 standard. That way it can use the Ethereum blockchain and is compatible with a lot of wallets and applications.