So what are the current “best practices” in long form blogging now in regards to visitor comments? Do you block new comments after X number of days, force people to register to comment? How do you keep comments (and trackbacks) from becoming spammed?

It seems like comments ought to be important, as part of the “conversation”. Sometimes people come late to the conversation but the post inspires a reply. But how does the blogger keep that communication open without drowning in spam?