Some interesting - if outlandish - predictions in this thread. Don't get me wrong - I wouldn't mind it one bit if my 500BTC end up being worth $500,000, but I just don't think that's realistic, especially in less than five years.
There's a lot to be said about crypto-currencies, but we are still in the early days of such things. Developers need to understand what users want, users need to understand what the cryptocurrency is, and merchants need to understand how to deal with them. A settlement network must be developed (which I guess is what Ripple is trying to do) and a lot of work to set rules, develop regulations and perhaps even laws will have to be put it.
Right now, we're in the wild, wild west. But we can't stay the wild, wild west forever.