Ripple is a scam to make OpenCoin rich off of other's evangelism. Luckily for them, it seems to be working.
That's not that simple. Their technological solutions are quite complicated, there were a lot of thinking and coding involved, so it's not a Ponzi scheme, they did some real work and plan to open source it for free, so anyone can easily create competing forks.
So I wouldn't call it a scam - it doesn't look like that.