Of particular note on the "more professional" front -- many HN members are here because they're connected to a YC company in some way, and many others are here

Of particular note on the "more professional" front -- many HN members are here because they're connected to a YC company in some way, and many others are here because they work in the industry and want to build connections with others also in the industry (but not linkedin-style connections; actual we-have-discussed-technical-topics connections). There are people here who have found work through the monthly Who's Hiring threads. The net result is that there's a strong professional ethos and strong incentive to maintain it from a lot of people in the community, such that the few who try to troll, post garbage, etc. tend to get voted down into oblivion and calmly told they don't belong.