I imagine that the totalitarians will declare all out war on bitcoin in just a matter of time, ostensibly as part of the war on drugs. I can already see the talking heads asking each other, "Can we really allow the use of a currency that allows people to make black market transactions?". So, I'll probably trim down my positions substantially in a year or two, depending on how fast our dear leaders seem to be moving on this issue.
It will still be a useful medium of exchange when it is criminalized, but a lot less people will want to risk having it around.
If that ever happens, watch out for whitelisted malware that looks for bitcoin-associated files on your computer and rats you out.
As far as I can tell, the only thing really stopping them from doing this is just their sheer stupidity. Who knows, maybe they are really so incompetent that they can't see this obvious workaround to their legal tender laws.