I know Seth from his Chicago days. Before SNL he lived here, then spent time overseas with a group called BoomChicago, then subsequently moved to New York. I agree he is good looking but I have seen his junk up close and personal quite a few times and it is nothing to write home about.
He and I changed in the same back stage area for a show we did at Second City over a summer. We played in one of the smaller stage areas with no air conditioning and it was often really hot, especially after we'd been running around on stage for an hour. We always brought clothes to change into and on more than one occasion I saw him slip out of his briefs to put on another pair of underwear and I always looked! I would guesstimate that he is 3-4 inches soft, give or take, very average size width...although I guess he could be a grower. Sadly, I've never seen him hard.
There is a rumor that has floated around here for a long time that he is gay, but I've never known that directly. I will say I never saw him with a girl, but he was always very focused on his career. One of the things that is kind of strange about the improv-SNL world is that gay isn't necessarily cool. Guys tend to keep it on the dl. Anyway, he is a great performer. He was not always the most generous on stage, but he was ambitious and it has taken him far.
His butt had hair on it too, but in a sexy way...not too much, if that makes sense.