As we discuss metrics, I would be remiss if I didn't point out that visitors are one of the easiest metrics to accidentally make a mess of. Here are some of the things that can throw off your visitor metrics:
• Your employees have your web site set as the start page when they open a new browser window
• Your HR department posted a job on Craigslist so potential hires are checking you out
• Your webmaster is updating the site and reloading again and again.
All of these will create spikes in your traffic and skew your numbers.