ya... as far from what i can gather from bitinstant... I put in US dollars, and get bitcoins... which means I have to guess about how many dollars I need to get the quantity of bitcoins I need to buy the coins.
It also means gas money, and getting cash in the first place.
Yep. Those pesky US dollars sure are inconvenient aren't they? Have to get them from an ATM or bank teller, then have to transport them by hand to the location where you spend them. It would be so much more useful if there were some sort of currency that had the intrinsic properties of a currency (rarity, identifiably, difficult (impossible) to counterfeit) but without the need to handle a physical object. Perhaps some sort of electronic/digital currency? Then you could simply transfer the currency directly to any other individual without having to get banks involved.
Bitcoin isn't your problem. The fact that you don't have them and are stuck with those US dollars that are difficult to exchange in a non-reversible way is where you are running into an issue.