Counte Dante wrote:
I tend to pay for most things (eg bars, resturants, MPs, stores, etc) in colones.  I've seen guys get screwed over paying those places in dollars.  Most non-mp working girls (eg del ray, key largo, etc) I have met always negotiate with me in dollars, even though I usually pay in colones.  I'm checking out some tico bars, so I will just use colones there.
Listen to the Counte.  Once, near the end of my trip, I paid for services at a local MP in USD.  I was screwed on the exchange rate.  Moreover, I got change in--take a guess--colones.
Use colones.  Now, if you bargain with a girl in USD, then you have nothing to lose if you have the EXACT amount.  Even here, I tip in colones.