(Update 2014-11-03) I liked the Octopress concept a lot but since it used ruby so much it was hard for me to customize or deal with any issues that turned up (I don’t know ruby). Also, I didn’t like the fact that every site you want to use with octopress is a clone of the repo. I switched from octopress to Pelican, which is python based. I found it much easier to understand and maintain. The plugins make sense and I was able to make my own modifications to plugins and themes after using it for only a short period of time. Everything I wrote below about reasons and advantages of switching from wordpress to static site generator still apply.
I recently changed this site from Wordpress to Octopress. Wordpress was getting to be a hassle to maintain, especially with needing to worry about constant security updates. I think I actually had the site hacked once and I had to rebuild the site to get it cleaned up. Then you have to keep a security plugin ... I just got tired of maintaining it.
I was running a plugin that monitors file changes, but I kept getting reports of 400 file changes because the web host was updating the WP installation.
The idea of keeping the site content in easy to maintain text files is very appealing to me. You can keep it all in a repo and it is easy to update, easy to track changes over time. It is very easy to write posts using markdown.
So, I switched to Octopress. It took me a little while to figure out how to set it up and get it configured. It also took me several weeks, working a little at a time, to convert the original Wordpress content into markdown posts. There is a lot of information on the web about how to do this so I won't repeat it here.
One drawback to using Octopress is that it does not have a commenting system. It does support Disqus but right now I do not like the idea of using a third party like that for comments. So for now, this site no longer supports comments.