So I went to one of the famous "line" eateries, where there is always a line, and you are lucky just to be in it waiting. This one is the greek deli at Dupont. It's so popular Kostas doesn't even need to give it a specific name, or provide any seating.
How good was it? It's good -- but realistically I think some have overrated it. It's quality, and the bread is baked fresh on the premises each morning. While I love this place, i would warn others that this is more of a case of an very good eatery that is relatively affordable, as opposed to a *great* experience. It has a peasant style feel to the food, each order an abundant amount that is sort of slopped together in the same tray.
The Gyro platter was a regular gyro with the usual green beans and a pasta orzo like side. The green beans and pasta had a similar taste and were very olive-oily and probably buttery. The gyro's bread was freshly baked and therefore a cut above most, but the actual sandwitch wasn't THAT much better than others I've had.
Still, overall, based on the relatively low price ($9-10), and portions, this is a good lunch extravaganza. Just not the 'best ever' that some reviews have hyped it up to be.