Early adopters will do well, no doubt, and have already done, but that's true for any new technology.  The guys that get in first make a motza.

But most people will want them for their utility.  That's what it's all about in the end.  Governments force us to to transact in their currencies by making them legal tender and blocking other currencies including those based on Gold.  That makes them high utility for many of us, (critically by force not choice) but as more and more trade migrates to the internet and becomes more global in nature it benefits having a truly global currency.  No country can provide this and, thank god, world government won't happen so it is going to take a market solution.  Hence, Bitcoin.

Whether it will replace government currencies I don't know, but it will take more and more market share from them as time goes on.  They sure don't help their case by debasing their currencies every chance they get either.   

It's just a great solution.  Better than Gold because it is more predictable.  Who knows where they will be able to get gold from as technology improves and we achieve true energy abundance.   But Bitcoin is a known quantity.  The best qualities of cash and gold without the drawbacks of either, plus improvements that neither have.