There's a nice little item on Daily Blog Tips about ways that bloggers evaluate their success, and the metrics that are available. If you've started blogging and are wondering, "How am I doing, anyway?" it's good reading.
They are, I think, overly kind to Alexa rankings, pointing out that they only count visitors with the Alexa toolbar installed (in other words - atypical users). I think anything that skewed is inherently worthless. And they mention the two metrics that I think are most useful for most bloggers: Technorati rank and number in inbound links.
Blogging is, after all, about the connections you make with other bloggers and being part of an online conversation; while it's obviously important that you have the right incoming links, a growing number of them is a good sign.
The most important point in the article, however, is this:
Each blog has its own unique goals that can’t necessarily be tracked by any particular ranking system. These measures and rankings are useful, however, especially in a number of situations that we’ll look at later in this article.
As a blogger, what are your goals? Do you want to sell products, make money on advertisements, promote and sell yourself as an expert on the subject, or do you just want to use your blog as an outlet to share your thoughts and opinions?
You don’t necessarily need a top ranked blog to meet your goals. With that in mind, don’t let ranking systems overshadow your goals.
Amen! If you're writing a blog about the latest insider buzz on clothing made from organic hemp, you are not going to be the highest ranking thing on Technorati or have a ton of readers. If you're writing that blog to promote your business of selling hemp fashionwear, that's fine; most of the people out there perusing blogs don't care about you and aren't ever going to buy from you, so the focus of your blog should not be on them.
But once you do know what you're trying to accomplish, this article gives you a nice roundup of the tools you can use to try to assess how well you're doing.