It really depends on the aircraft, that dictates how much ‘extra’ legroom you get in the exit rows. Obviously if there is a full size door there, like a 747, you have more legroom than in business class. Typically on narrowbodies, you have the one or twe overwing exits, so they just make the row wide enough to accomodate people having to walk through there. On UA’s 757’s, that amounts to A LOT more legroom. On their A320’s, however, it’s probably only a few inches more. On their 727’s, when they were still around, they had about as much room as the 757’s did. Now, on their A319’s and 737’s, they only have the one over wing exit, and they basically have one seat missing right next to it. I really never saw the logic in this, but nevertheless, that amounts to a total of 2 seats immediately behind that missing seat that have an enormous amount of legroom. This last summer, I rode on Virgin’s 73G and 738, and I don’t recall off the top of my head, how they have the exit rows configured, but if I’m not mistaken, it’s in a similar format to UA’s A320’s and 757’s, where you have 12 seats (6 on the -700) that have a few more inches of legroom.