It's already been stated multiple times here, but there are far too many "acceptable" examples of currency substitutes being employed by various parties in the US.  The US Government finds fault only with the Bitcoin because it is often used in underground trades for black market merchandise.

I will forecast that, although they will try to shut down .onion sites such as The Silk Road (which might've already been accomplished, given the look of it), they won't attempt to touch the Bitcoin.

Hello, aspiring miner from the USA here.  I've been using Tor for over a year now, but only recently stumbled across this underground currency market (which I find incredibly fascinating, btw).  Looking forward to (hopefully) making a big dent in a Bitcoin block!

Well, being a newbie, might as well start here!

Such restrictions are not unreasonable.  I imagine this has been brought up before, given this topic has accrued 20 pages, but new members should be expected to demonstrate some sort of commitment to the forum before being allowed to have an impact on discussion, bitcoin trades/games, etc.  This is a forum, after-all, not simply a stepping stone to bitcoins.