It's a mistake to think in terms of USD profit. Did you forgot than Bitcoins are themselves valuable?. Furthermore, even if you don't care for Bitcoins, no one is obligated to sell at the current market prices, that's actually the stupidest way to go.
Why? Chances are good (if you're in the USA) you bought your equipment in USD, and you almost certainly pay your utilities in USD. It also makes a good frame of reference, even if you do only consider the things you can buy in BTC.
If Bitcoins are worth $15USD, most people who are selling stuff are going to price an item that they value around $15 at or near 1BTC. So I don't really see how not thinking about USD helps at all, if anything it just throws off your frame of reference considering the wildly fluctuating value.
1BTC right now is not the same as it was a while ago, and it's probably not the same as it will be in a month (for better or for worse), the changes in value of things measured in USD changes much less dramatically.