I used Express Pool to get from K Street in DC to Dulles the other day -- $18 vs ~$35 for pool vs $54 for UberX. I had time to kill so at that rate it was worth seeing what it would cost to save $36. I was asked to walk from 1629 K St NW to Connecticut & K (about a 3 minute walk). Driver was clueless about the fact that I had been told to go to a specific corner. We were supposed to pick up another passenger, but someone must have canceled -- because I ended up getting the ride to IAD solo for the $18 (and was working on laptop in the car anyhow). What a steal. (And, as expected, I was dropped at the normal IAD dropoff area because where else would they drop you, out on the tarmac somewhere?)

Tried it again another time to go a short distance in DC but the 3 minute walk on each end was very not worth it. I'll definitely consider it to or from an airport if I have the buffer.