Manipulate the User Agent for Accurate Site Stats:
"If you implement any sort of hit monitoring or tracking on your Website, you probably don't want to include any of your own hits."

Ordinarily, you could set a "self-specific" cookie. Then, when the tracking script was called, you could simply check to see if that cookie existed, and, if it did, exit the tracking script.

However, if, like me, you're frankly scared of cookies on the grounds that they:

are difficult to test with,

are called something silly and

aren't 100% reliable

Furthermore, many Webmasters exclude from tracking certain browsers that are known not to work on their Websites. For example, many sites block any non-Internet Explorer or Netscape browsers, such as Mozilla's excellent new Firebird and a whole heap of others. Being able to manipulate the user agent to fool the Website into thinking we're using Internet Explorer 6.0 when we're really running Firebird 0.7 could be quite handy! …

http://www.sitepoint.com/print/site-stats-user-agent