The use of tags on websites to call content or advertising has increased. While providing more opportunities for providing content and targeting, tagging can also give away your visitors' information and your stats.
It is not rocket science, but you should make sure the code is clean and that there are no conflicts. We have all sat looking at a white window while a slow site loads. The site is probably undergoing "tag overload."
Whenever you are finished installing tags, check your site's load time from several computers. If you watch the left side of the status bar, you will see the name of the application that "hung."
The IAB is working on a draft best practices manual. They have released a draft for comment. View or download the PDF file here: http://www.iab.net/media/file/SiteTaggingBP_v1.0.pdf