WordPress.com has some nice stats (click on Site Stats under Dashboard) about traffic on your site. Unfortunately, those stats aren't as fully featured as other analytics services such as Google Analytics, which is available to WordPress.org users, and discussed later in this section. Nevertheless, there is plenty of useful information that you can derive by looking at the stats. In particular, you can see graphs and data on the following:

This data can also be chopped up by day, week, month, year, or all time, which means that you can make fairly accurate measurements of the effect of your marketing campaigns. For example, let's say you write a blog post and share it on Stumbleupon.com and Twitter. After giving the article a few hours to circulate, you come back and check the Referrer stats for that day. You should see Twitter and Stumbleupon listed alongside the number of visitors...