Ever needed an SMTP server to use for testing, but you really didn't care if the email actually went anywhere? If so, be sure to check out Neptune (http://donovanbrown.com/post/2008/10/20/Neptune.aspx)
It's a cool little tool from a buddy of mine, Donovan Brown, that allows you to test SMTP functionality without having the SMTP actually relay the message further. I will definitely be putting this to use very soon myself. I don't know why someone didn't think of this earlier, hell I could have used it last week!