UPDATE - here's what I initially wrote about this plugin...
Just another professional-quality highly effective piece of code from these guys. Insanely simple to load and activate with ONE setting required: "Enabled/Disabled".
Yet, if you want to totally geek-out on the tweaks, they are all there with a MASSIVE amount of explanation. I learn more about WP internals just reading the comments of code written by these guys than the codex.
When I went to my live site to see it work, frankly I was floored. That page loaded so fast I thought I was in a localhost sandbox. And if you're ever in doubt about the cache status, there's a "Clear Cache" button on the admin toolbar that just clears everything.
I am going back to all my websites and replace other cache plugins with this one.
Now I have to say that I'm looking for a replacement. As far as I can tell, this one works fine, but features that I had in the past have now been crippled and are enabled in a "paid" version with the release in December of 2013.
As far as I am concerned, this creates a HUGE amount of ill will among people who loved this plugin and the developers. If it were me, I would have released a totally different product and kept this one at the same high level of quality that it used to be.
I have to say that I am really saddened by this.