If you use MSN Messenger and drill into its properties, you can tell who's still got you listed among their contacts. It's only nominally interesting information, save when you piss someone off so much that they actually delete you.
(cough)
There they are, a half dozen people I worked with for a few weeks a year ago. As soon as that job ended, I deleted them from my contacts. Yet there I remain, cluttering their contacts lists. They likely get a stupid "toast" message every time I reboot. Why? Why on earth? Clingy-ass people! Belinda, I'm not coming back. I need you to let me go.
Best use of the blocking feature ever.