The closest I've personally come was dancing a bit with a girl, getting her number only to have her get pissed at me and move on to another guy because I was more interested in the fact that they were playing an unbelievably awesome version of "In God's Country." Not to worry, though, she wasn't just some hot girl at the bar who came to drink and get picked up, she was a fan. She was legitimately pissed at my reaction and said "I could see if it was Bad or Out of Control, but don't ignore me for a mediocre song." I would consider not loving IGC as a deal breaker anyway, so its not like she broke my heart or anything.
Wait....that is a true story, but it happened at a bar in Boston a couple months back when I was seeing The Joshua Tree, a great local tribute band.
To answer the question in a serious way:
I am 23 so not the youngest U2 fan, but definitely on the younger side.
Even at Vertigo when I was 18, I noticed a lot of attractive girls my age, more so last year on 360. Seriously, it really made me happy to see that U2 was so popular among attractive college aged girls after seeing so many of them glom on and sing along to their DMB loving drunken frat boy boyfriends for 4 years.
If I am early 20s and can find a lot of possible candidates so to speak, then probably anyone who goes to see U2 on a regular basis could find pretty good pickings in their demographic.
I would say the biggest obstacle to this one night stand thing among us blue crackers would be this. Think about it- if you are going to get things to the point where the person is going back to your hotel room, house, car, what have you, that would require missing/not fully paying attention to a hell of a lot more of the show than any of us here would tolerate!!
Unless of course you meet someone in the GA line at 6AM and you are already good friends by the time it gets too loud to talk w/o leaving the immediate area of the show.
Your odds are sure as hell better on this tour with all of the stadium attendance records being set! You have 3 to 4 times the chances you had at any given arena in 2001 or 2005!!