Had a situation here and I thought I'd take and informal poll and see if this seems to be a wide-spread IF bug or not.
When I didn't get the last bulk email that was sent from BB, I checked my account in the ACP and found that my email field was blank, which was strange as neither Cory or I had removed it. I also did an ACP search on my own board and found that I have 7 blank email addresses there (out of about 78 members).
I'm curious if any of you have noticed this happening on your boards. You can find out quickly by searching the member list this way:
Find/Edit/Suspend Users > Member Advanced Search :search
Members for _
(finds entire member list)
Find/Edit/Suspend Users > Member Advanced Search: search
email addresses for @
(finds all members with an email address listed)
When the board returns your results, you will see a search results number at the top of the list:

If you subtract the number of results of the email search (@) from the number of results from the member search (_) that will tell you how many blank emails there are.
I know that users can erase their emails once they are registered, but I don't think that's the whole story since that isn't what happened here. I also remember someone reporting a problem like this in the IF support forum.