Installed and setup w3tc last night (switched from Quick Cache) and seem to be having good results; raised my google page speed from average of 80 to 85-87. I wanted to see what else I could do so I tested it in Pingdom (got 80/100) and now I'm going through the items I can fix.
The following resources are missing a cache validator. Resources that do not specify a cache validator cannot be refreshed efficiently. Specify a Last-Modified or ETag header to enable cache validation for the following resources:
Is there a way to specify a cache-validator for these non-wordpress resources? Maybe in .htaccess?