Like with software, I don't think people will care much about the Open Source aspect, but I do like the Free part in the sense that the free software guys use it (libre): that it's YOURS, unencumbered, and you are free to do what you want with it.
"Free Money" might even work better than it does for the free software guys. Here it won't be mistaken for free-as-in-beer.
Hehe, I have read quite a few comments by people new to bitcoin who think that Bitcoins are free because you can mine them.
But in a few sences they are free, in that you can get them by mining them even if you dont have access to an exchange and that no banks or credit card can freeze them.