Another solution could be to create a block for each AD where all *interested users* in this AD are listed. 

The same principle (listing interested users) is allready used with the EVENT module, there it is called GOING. So LeonidS may I ask You if such a listing is also possible for ADs?

People would like to see who is interested in an AD. Also for the AD owner it would be great to see all interested users in one place.