Actually, I think this is likely the best way to deal with trolls. Having someone input their credit card gets rid (at least in their mind) of the anonymity that trolls thrive on.

The majority of the anonymous-posting news sites I have visited have been filled with trollish, often misspelled comments (on a side note: I think there must be a direct relationship between how poor a speller one is and their political leanings..). The NYTimes is the only major news source where I have found the majority of the online comments to have been written in a legible manner.

If HN grows too big or unruly to manage, I fully expect pg to implement credit card registration as well...