This is a question for anyone else who has both an affiliate banner near/at the top of their web pages and another (different) affiliate banner near the bottom of their pages. Do you see a vast difference in the number of clicks on your top banner versus the number of clicks on your bottom banner?

Obviously, you, as a webmaster, want to place the banner that will do better or that you would like to do better preferentially near/at the top. But there have been many months where my top banner - no matter what the product or service featured - has gotten 5 times the number of clicks of my bottom one.

To anyone who monitors their affiliate traffic closely, what have you yourself noticed as far as comparative clickthrough rates are concerned?