These generally work much better than an ad swap because you are also getting a personal recommendation from the publisher. Since the publisher is known by his readers and hopefully has some credibility with them, they react positively to his recommendation. Your readers are constantly looking for other quality ezines. They will appreciate your recommendation, and the other ezine publisher points out your quality publication to his readers. Link and banner exchanges are cooperative efforts that we are all familiar with.
Links seem to work best when they are woven into the text of a page.
Using banners effectively requires a lot of testing and adjustments. Both methods can bring in lots of highly targeted traffic when placed on appropriately selected websites. These are just a few of the traffic building methods that can be supercharged by working cooperatively with another webmaster. Virtually all of the other traffic builders can be used in a similar fashion. For example, you could offer free ads in your ezine or offer free programming services in exchange for another webmaster writing and sending out a press release for you.