One of the better things to pay attention to other than visitor traffic is who is linking to your site. If you are getting a large amount of linkage odds are you’re doing a good job on developing your site (unless of course every site that links you has “sucks” at the end of it’s URL name). The easiest way to check who’s linking to you (besides looking at your pingbacks and trackbacks) is to google yourself. The more specific version to look at though is Google Blog Search. While regular links on websites are good to know about, it’s what people are saying in their personal blogs and forums that gets you the real meaty information about how you’re doing. I definitely recommend doing this at least once a month to see how far out your site has reached into the Internet.
There’s also the possibility that you might find someone using your content illegally, so that’s good to know also.