pg has stated that YCombinator is looking for good/great people, even if their startup idea is weak. He's also stated that skimming your HN comments provides one way to judge what sort of person you are.

Most high-karma people on HN (like, 5k+) get there by being thoughtful. I'd imagine pretty much everyone in the top 100 would be helped rather than hurt by their HN presence. I suppose it's theoretically possible to amass a lot of karma without making any useful contributions, but I haven't see anybody do it yet.