A Google Groups thread discusses a classic SEO challenge, passing link popularity for tracking URLs. Honestly, I cannot sum up the issue better than the original poster:

How can this webmaster keep the tracking capabilities but at the same time, keep the link popularity to the main URL?

With Yahoo, they give you a tool within Site Explorer named Dynamic URL Rewriting. This tool allows you to tell Yahoo that these dynamic URLs really refer back to this main URL. You really do not have to do any coding on your site or server to communicate this to Yahoo. All you do it plug in the information into Yahoo.

With Google, it is not that easy. In Google, you need to make sure you set up your site and server to communicate this to GoogleBot. JohnMu, a Googler explain:

There are other solutions, but they don’t work as well as this one.

Forum discussion at Google Groups.