TTFN: Slate's Matthew J.X. Malady thinks it's time to get rid of sign-off lines ("Regards," "Best," etc.") in emails.
I generally only include them when it comes to dealing with relative strangers, or in emails that are of a length and structure that they function as letters. Sometimes, I'll do a vestigial "--Adam" at the end of an email, but since each email address I use pretty clearly identifies me as the sender, I recognize it's likely superfluous. You?