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.
This isn't completely accurate. You only have to accept USD from someone who owes you a debt.
Correct.
Here is a source for the skeptical:
http://www.treasury.gov/resource-center/faqs/Currency/Pages/legal-tender.aspxAs with many things in law there is a fine distinction. You can agree to contract for whatever terms you like and you are generally not forced to do business under terms you don't. What legal tender is dealing with (in the US, in other places it might be different) are debts already created.
An effort to force people to accept USD when they don't want it would have preverse effects like not being able to sell tickets to events (wtf! you must let me in, here is USD!!) or other stupid things like "here is an armored car of pennies, give me your car now, I don't car that you only wanted to trade it for another similar car! Legal tender!"