I agree with most everyone here but there are a couple good points this discussion brings to light.

For most of us, Bitcoin is priced in (not backed by) USD... just like oil and gold are priced in USD for much of the world (China and Russia are changing this).  But Bitcoin is used worldwide, and we're free to value it against whatever currency or commodity we'd like.  That's part of the beauty of it, Bitcoin is a means of barter and it only takes two people to decide "how much" and "of what".  When the dollar loses strength (aka, becomes less desirable), people will naturally want more USD for each BTC, or they may decide they don't want USD at all and start trading BTC for something else.

The flip side is that Bitcoin is not backed by anything physical, but it is backed by the support and efforts of a fantastic community and definitely has better fundamentals than any fiat currency.