All coinbase users that didn't pay taxes on gains after selling their BTC or trading alts are F*'d up.
FTFY.
Or do you have to pay taxes on a yearly base regardless of whether or not you've liquidated your assets in the US?
Good question, actually. Don't have an answer for you :| To my understanding, there is only a tax obligation upon any realized profit or loss, but what do I know.
EDIT: OMG. Apparently every time you move a BTC off Coinbase to your wallet, that counts as a sell event.
God Fucking Damnit !