I've got it implemented on one of my sites and it seems to do nothing. Although I do not fully utilize it. My CSS and java are still coming from the original files. I do have a subdomain setup for CDN but havent changed over yet. My site is in the development stage so I'd like to have a SOP in place before my content gets out of hand.
Side note: I'm using Thesis Framework on another site and it seems pretty darn quick. Both sites are on the same shared hosting.
If you dont mind posting your W3TC setup/procedures, I'm sure a bunch of people would be greatly appreciated.