I have been using W3TC on a site with 70k unique daily...and works like a charm.
I tested it on another install, and pages aren´t been cached (using disk cache), I get a message "cookie is rejected".
I tried this on three different computers, that have never been logged in.
I enabled debug and noticed that every query said "cookie is rejected" :
Caching (Reject reason)
| disabled (cookie is rejected)
W3 Total Cache: Db cache debug info:
Total queries: 191
Cached queries: 0
Total query time: 1.062
W3 Total Cache: Page cache debug info:
Engine: disk (enhanced)
Reject reason: cookie is rejected
Status: not cached
Creation Time: 2.675s
X-Powered-By: W3 Total Cache/0.8.5.1
Content-Type: text/html; charset=UTF-8
Any idea on what could be wrong?