I just utilized this feature of Gmail and thought I would share it.  I came across it on a blog this weekend.

For a blog post I just wrote for the VBS Blog, I invited folks to join us as guests for a day at CentriKid Camp.  I put my email address as normal so they could contact me, but I modified the hyperlink for my email address to "+campguest" at the end.   Gmail ignores anything after the "plus sign" so it allows me to set up a filter within my account based on that specific address.  I want to make sure that anyone responding to that blog post got top priority and visibility in my inbox.

This trick can apply to any sort of message that you want to be sure SEE, or be sure NOT TO SEE.  Give it a try!