Social networks are useless with pseudonimous accounts - unless there is some link between pseudonyms. The social aspect is in building the network, having reputation, maintaining a circle of friends and acquaintances, etc. but you can't build network out of throwaway accounts. Of course, HN is not a social network - it's a news/discussion site. So if you don't care about the reputation - which is not prominent anyway, so there's not much reason to care - you can use throwaways freely. But for most social networking functions it's a no go.