I have been using W3TC for several years. It seems to do a lot of things to make the site faster and in some cases, it does the job well.
But now, for the third, or fourth, or fifth time a simple upgrade completely hosed me -- I couldn't log in to admin, and needed to manually deactivate the plugin.
My impression is that this is a case of trying to hard to be everything to everyone. Now I'll run PageSpeed and YSlow again, see what is slow and fix specific problems with simpler solutions that work.
Sigh. I know the author has done a lot of work and tries hard to make this a really killer plugin. But in the end, I have had nothing but trouble for a modest performance improvement I can get through other simpler methods.