Great question! I cannot wait to see everyone's responses!
Sometimes I will subscribe to email notifications.
Another thing I'll do is use Google Reader to keep track of posts I comment on. Under the "Goodies" section of the settings there are bookmarklets. I use the one for "Note in Reader", which is basically a way to share or bookmark a page in Google Reader. After commenting, I click "Note in Reader" and then assign a "commented at" tag.
That makes it easy to go look through your commented tag and revisit posts to see if there's been a response.