I used to use BugMeNot regularly, and keep a few “throwaway” email addresses for the reason mentioned by weareknights.
I also use throwaways for testing other people’s systems. I’m going to shortly be testing a ticketing service and a story-uploader-- no way am I going to use my real info for some site’s accessibility testing.
However, I think the majority of throwaway emails encountered by WP admins are spammers rather than spam-avoiders. I can see this being useful as one tool among the arsenal they should be using.