Why wouldn't you pick a seat when you signed up and paid? This happened at Quakecon also, people paid their $30, but had to wait in the long line because they didn't actually pick a seat... Seems silly to me to pay for a reserved seat and not pick one ASAP, even if you're waiting for friends, pick an open spot and anticipate them sitting next to you...
Just my $.02
Lesson learned: Pick your seat, and people will sit next to you