Sometimes you may notice a URL listed in the search results page that may look like www.domain.com/?tracking=5 or something like that. You normally do not want to see your pages with URLs listed in the search indexes like that. It is bad for a few reasons, the two most obvious include (1) you are tracking results (clicks/conversions/etc) from a different source (Google is most likely the source you did not want to track those clicks from, in this case) and (2) the link popularity of that page is somewhat off according to the search engine.
This use to be a bigger issue with search engines, today it seems to be slightly not as big of an issue.
So what remedies do you have?
A WebmasterWorld thread discusses 301 redirecting the tracking "URL to the same page URL but without the parameter." The other solution given is to add a noindex meta tag to the page with the extra variables (make sure it is only on that page and not on the version without the extra variables (often harder to implement).
Best solution of the top two? 301 redirect.
Best solution? Get the main URL indexed.
Forum discussion at WebmasterWorld.