I am working on a wordpress installation for a client that is using the latest w3tc on wordpress 3.4.1. I have set the expiration for garbage collection to 3600 secs or 1 hour and even though the client has updated some information on a page for their customers it was not updating even after 24 hours. I ended up having manually purge the cache for them however they are still experiencing this same issue. wp-content/ is 777, wp-content/w3tc/ is 775 and all files inside the w3tc directory at 755 as they were created as automatically. If you need any other information, please ask so I can try to figure this out. Thanks!