A lot of blogs today rely on plugins that operate on the "the_content" hook to add content before and after their posts. They are adding simple code and rarely are the plugins ever really doing anything the "real" content. As much as I really don't like the theme pack: Genesis has a hook for before and after "the_content" and I recommend a real hook be placed for WordPress itself.
Plugins will no longer have to slow the execution time by replacing "the_content" over and over again which has led to the most common performance drag I've seen in all of my clients.
Hook Executed before "the_content"
Hook executed after "the_content"