Works very well. Read the instructions carefully as some themes/plugins WILL BREAK with certain options enabled. Simple to use, easy to install and get working. Gives tons of valuable information and performs several useful functions (like regular backups which you should be doing anyway). Overall, a must-have plugin for any site.
EDIT (6/9/14): With the move to iThemes, this plugin no longer has my vote as an exceptional plugin. Every one of my sites broke with the update and now the dashboard is spammed with messages. I've met the developer on a few occasions as I reside in the same city and have always appreciated his contributions to the WP community. Unfortunately, I can no longer recommend this plugin to others and will be searching for something else.