I think you should be clear: using/possessing bitcoin right now is not a legal grey area, it is very clearly legal.
not necessarily true for merchants.
Merchants are
allowed to accept alternative currencies/other stuff in exchange for services/goods, but they HAVE to accept USD by law.
Where this law is written down? It doesn't make any sense to me. If I want to sell my computer and I put an ad on Craigslist saying that I'll only accept a trade for a car, that's illegal? Also, even if this is law, what's stopping me from selling hamburgers for .5 BTC or 50 USD ? I would accept both then, wouldn't I?