This is just my opinion after using this tool in depth for 3 months.
- Fast as all hell once configured
- Hard to configure
- Hard to maintain
- Hard to support
I recently uninstalled it from my high traffic site and went back to Wp Supercache.
I had to uninstall, then install and uninstall a couple of times because of it's temperamental nature.
WP Supercache is fine and fast too but it's more of a stress free plugin.
If you have a website where you need to focus on content, WP Supercache is the one for you. If you want bleeding edge performance and are willing to keep an eye on server configuration all the time - W3TC is for you.
I think that this plugin is waaay too much hassle for the average website owner. It's more for people who have dedicated technical resources or the time and interest.
Just my 10 cents.