How Often Do You Change Your Promo Materials?

Lets say you are promoting 1 or 2 sponsors really heavily, you throw up some banners or text links, whatever and send your traffic to the sponsors site.

How long do you keep using the same promo materials to send traffic to the same sponsors paysite?

It would seem to me, that it makes sense to periodicially change out promo materials so that it stays fresh to the surfer, especially if you have a site that gets bookmarked traffic.

What are your thoughts on this and also, how many affiliates do you think actually spend time to swap out their promo materials on a regular basis?

Regards,

Lee