The only things that really make me question Seth as a person is the fact that on the Cartoon Geeks podcast, noted animation fan Michelle Klein-Haas felt that Seth came across as a creep in an interview, and my gut tells me that that there may be just a bit validity to her feelings, and some people on TV Tropes feel that Seth's DVD commentary rant (about the Simpsons gag on Family Guy being cut) is a sign of egotism. On a related note, I definitely disagree with his opinion that the long, drawn-out gags on Family Guy are gold (those kinds of gags are easily what I hate the most about Family Guy)
Frankly, I have more disdain towards the current Family Guy writing staff than I have towards Seth himself, or the writing staffs of American Dad and Cleveland (I find American Dad to very enjoyable, and while some earlier Cleveland were pretty bad, it has gotten better to the point that I feel it has become a worthwhile show).
That kind of thinking works in some industries, but I feel when that line of thinking is applied to the entertainment industry, it more often than not leads to homogenous, unoriginal productions (like the umpteenth horror film remakes, and now even films based on board games, of all thing) that are IMHO the dearth of quality in Hollywood.
Case in point: Pixar seldoms make the same kind of picture twice (though some may disagree), and their ambition (which often spits in the face of the same bean counters who felt that Up wouldn't be a success because an old man wouldn't make good toys for kids) is largely what their films so special and celebrated.
Well, I've ranted enough.