Value in government money gets inflated away. Sure, someday that will probably happen. Someday, our entire civilization will collapse (every civilization in history has done the same). Unless you think we're close to a total collapse of the global financial system, your money isn't going anywhere, especially if you put it into non-currency investments. If you do think we're about to fall off a cliff, then your Bitcoins will be basically worthless because we're about to enter a period of relative lawlessness with greatly reduced access to information and the Bitcoin network probably won't survive (or the Bitcoins will be plundered by rogue information-pirates or something weird like that).

If you want to mess around with Bitcoin, awesome, but please don't see it as more than it is: a toy for the privileged.