Though this is an obviously technically complex plugin that's trying to do a lot, I found that it was designed in a scatterbrained fashion, with many settings in no particular order. I'd suggest some professional QA and a hierarchical set of menus that offer a simple but effective implementation for beginners, and a get-out-of-my-way interface with plenty of control for experts.
On install, I got messages asking for various missing files. On updating WordPress, I again received messages asking for missing files, or for me to delete other files. When another plugin misbehaved, I had trouble fixing the problem because W3TC had cached a corrupt file, but dashboard was down. Normally, I'd just FTP the file but once it's cached...
On deactivate, I had another missing file, had to FTP changes to get the thing out of my system.
I have to say that there was a substantial speed increase, once I messed with it for a few hours.
On update, it obnoxiously and unmercifully bothered me until I agreed to tweet or friend the CEO! I mean, every time I clicked on something! Then when I added it's link to footer (No problem, BTW. I'll support you while I try your software, but try to be less obnoxious about it next time.) Unfortunately, the link W3TC added to my page was an obnoxious colour and not in the area for links in the footer. No, that's not good enough for W3TC. God forbid someone should be allowed to change the link colour to fit their theme! Oh, no, W3TC has to add it in a roundabout way so you can't change it! Annoying.
The last straw was that on doing some research, I found out that W3TC has some functions that overlap with CloudFlare. One can simply dump W3TC and get as much improvement, at least in my case, by enabling the Cloudflare functions that don't play well with W3TC. I did that, and ended up with 90% of the speed, without the errors, missing files, overhead, and obnoxiousness.
Goodbye W3TC! Call me when your interface is ready, you've caught some bugs, and you've toned down the obnoxiousness.