At the same time, it could also be the best currency for tax evasion. (You don't need middlemen or authorities in order to send value.)
It all depends on what the user wants, and whether or not the user is competent in achieving those desires.
Perhaps this will usher in a new form of taxation where taxes are only paid by those who support the projects/governments for which those taxes are earmarked. Perhaps "taxation" will become a type of pay-as-you-go system and will be more focused on results instead of promises. Who knows?
I think it has both pros and cons for both legitimate tax paying and legitimate tax avoidance. One thing for sure is the tax man is going to have to learn to live with it and find ways to deal with its use because it isn't going to go away any time soon so they might as well try to work with it.