Blogging is so much more than about expressing yourself; it can also serve as a learning tool.  I have learned many interesting things through blogging.  Here are some of the ways that use my blog to learn: 

First, writing is mental exercise that, if done carefully, forces one to think about how to clearly present an idea.  What kind of facts or information does one need to defend a stance?  Can that stance stand?  What are the best words to use>?

Second, a post's comment section is a great way to expand one's horizons.  Not only do others provide feedback, but sometimes they include links to either their own site or other relevant sites.  Sometimes following links left in comments is a great way to find other people who have more information or share a common interest.

Third, analytics programs also help point to other sources of information related to a blog.  If another blog or site is linking to a blog, there's a decent chance that at least the post or page in question is related to one's blog.  Like comments, following sources of traffic one can find a whole community of people who share a common interest.

Fourth, linking to other bloggers and sites that you find useful information also helps one learn.  Blogging is about conversation and writing a post in response to another post (while linking to it, of course) is a great way to debate and collaborate.  Comments and analytic programs can aid in this conversation process.

What are some other ways that one can learn through blogging?