You may think that being in the middle of Africa, US dollars would not be the popular currency. DRC is in fact former Belgian colony, so wouldn't the Euro be the prized foreign currency? Oh no.
I use US dollars so much here that I actually haven't and won't be exchanging currency. The local currency is the Congolese Franc which I've seen in denominations of 100, 200, 500 and 1000.
With an offical exchange rate of 925 francs to the US dollar, you can imagine the stacks of money one would have to carry around to be able to pay for anything.
Here in Goma, the exchange is actually 1000 to 1 to facilitate transactions-- especially considering that I haven't actually seen anything less than a 100 note($0.11).
The only reason I have seen this currency and carry some in my wallet is because the francs are used as change. For instance, if my grocery bill comes to $25.40 and I pay with two $20s it is likely that I'll get a $10 bill and the rest in francs. And, it is expected that if something costs $1, you can pay with a 1000 franc note and not expect any change.
Oh, the joys of money.