As a person who wants to hedge against inflation or hyperinflation, it has a fixed total supply and can't be directly manipulated by the government (nor does its value depend on the government's credibility).
As a speculator, there is the _possibility_ of making huge profits if you go ahead and get in early.
As a person who is afraid of government power, it _could_ take away a lot of the government's power if widely adopted. (If everything is "cash," they can't really tax you accurately; and with Bitcoin, they can't just print more money.) It would be really nice if the US government had to choose between, say, multiple decade+ occupations in the Middle East vs. spending on other things.
As a regular spender, there is the _possibility_ of easy digital transactions with less overhead expense (e.g. swipe your smartphone to pay for something, _without_, say, VISA taking off the top... though probably it would be some bitcoin processor taking (less) off the top).
A different way of looking at it is: it's basically analogous to gold, except easy to transmit, but not impervious to apocalypse or regulatory action that would take down the Internet. Basically everything I said above is an implication of this way to look at it. People who are slightly bullish on gold ought to be extremely bullish about Bitcoin, IMO, if they have the technical understanding to believe that it works (I do, and it does).