I can't believe I ever ran my site WITHOUT this tool. Very easy to set up, with thorough documentation, I had it running within 15 minutes. That process REALLY opened my eyes to how many basic changes you can make to your site to help increase security - along with many more sophisticated means as well.
Using this tool has also shown me that security paranoia is well justified. My sites - which have only low to moderate traffic - are the targets of basic hacking attempts several times each day (I had no idea).
While using this tool is clearly not the magic bullet for site security, it gives you a big boost in the right direction.