I had this problem as well, I even started a similar thread (http://forums.digitalpoint.com/showthread.php?t=61708) . But then I started using some of the techniques in this thread (http://forums.digitalpoint.com/showthread.php?t=61789) and the targetting has been a little better. I still get some off-topic ads but nowhere near as bad as before.
Nah. My link units have been running fine for months and months, then suddenly out of the blue they're no longer targeted or not appearing at all.