With all due respect to the time involved to develop a plugin with as many features as W3TC, after installing it on 3 different templates, I must confess I am disappointed in the performance.
Perhaps if I was running a simple two column blog with a few images and widgets things would be fine, but that's not the case. Msybe my expectations were too high, but nevertheless here are the problems that I have encountered with the current installation: I am using PageLines Platform Pro Framework theme.
1. W3TC and Google Adsense Text/Image ads don't get along: the ads have completely disappeared. I was using a widget for this, but even when I put the code into the sidebar manually, nothing shows up.
2. The caching of static content is miserable, I have page and browser caching enabled, object/database disabled, but 44% of my site content is not being cached.
3. The overall page loading speed is 8.1 seconds -- way too much time. W3TC has had no impact on this at all, in fact the site was loading faster using DB Cache Reloaded Fix.
4. W3TC apparently conflicts with FeedWordPress.
The dearth of plugins that work with WordPress 3.1.2 in the critical areas of caching, image management and the other features that make a blog competitive and user friendly is driving me to learn how to develop/upgrade plugins. On average for every plugin that I find that is compatible, there are 10 that are not.
I personally am about at my wits end with the conflict between the standards of website optimization tests such as webpagetest.org and the performance and configuration of themes and plugins. The time I have spent searching for the methods to resolve the problems generated as a result of this is overwhelming.