I am a big proponent of having an empty email inbox. There is just something Zen about a clean slate. But what do you do with those items that require follow-up work? I recently set up a free Gmail account along the lines of firstname.lastname@example.org (that's just an example, so don't try to be clever and spam it!). Any time an email requires a lengthy, thoughtful response, I reply with, "I'll let you know by XXXX," and BCC my follow-up account.
I also have a rule set up in my email software that moves all messages sent to the follow-up address to a 'Follow-Up' folder. A few times a day, I review that folder and clear my follow-up items. It saves me time, ink and Post-Its, and it also gives me a Zen-fully clean email inbox!