What exactly are they, how do you do them, and who do you contact to place them?

Hi,

The ad-swaps are generally announced by the webmasters in a mail or in their news or support forums.

Webmaster abc tell his/her members that if the members ask webmasters xyz from other sites to send an ad for their sites, abc will send an ad for sites xyz for free.

Generally members run to all the webmasters asking if they are willing to send an ad for site abc (with if possible reflink from the member asking of course ;-) ), so they'll have their site promoted at site abc as well.

A good way to motivate members to find downlines, members with downlines become more loyal, click more etc...
A good way as well to have a bigger membership.

The problem is that if everyone offer ad-swaps all the time ... webmasters will be overwhelmed with mails from members asking for ad-swaps and it cost them money to send the ad anyway ..so more and more webmasters will have to refuse it.

Webmasters make ad swaps with fellow webmasters as well sometimes to have refs for their Gold-members... well, I think ... ;-)

Sophie