I used to be big on doing adswaps and in fact used to run a network for publishers to do solo adswaps (long time ago) but rarely do them anymore. I recently had someone consistantly bugging me to do a swap with them, the answer was flat out no, because I knew they over mailed to THEIR list, so nothing of value would've come out of it on my end. Then they started giving me attitude about it - bye, bye!

No good can ever come from over mailing to your list.