Maybe. We send out a newsletter once a month and for the end of 2008 and all of 2009, we've had between 10-20 or more email bounce backs each month. While some of those could be bounced back for other reasons, our assumption is that the person is no longer at their job. Keep in mind that most of the email addresses in our list are business addresses and not personal home email addresses.
So a few days ago I sent out the January 2010 newsletter and I only had 3 'user unknown' email bounces. December 2009 was under 10, but only a little. A definite improvement.
Here is the January 2010 newsletter if you are interested:
I guess I could call this the "Email Bounce Economic Index".