Google Analytics has been around since November 2005 offering free analysis of traffic for website owners. As well as basic page visits it will also track search terms, referrers and pay-per-click advertising.
Although a very complete service, one constant criticism is the reporting delays. Typically GA reports on site traffic several hours, and in some cases, 24 hours behind. In the fast moving world of the internet, and especially in social networking where stories break in an instant, this delay was considered a hindrance.