The wp_cache_get API has 2 parameters that are not presently being handled in the W3TC ObjectCache implementation. Other plugins and possibly WP depend on these parameters. Not properly implementing the current API could break or at least erode performance of WP and/or plugins.
The missing parameters are $force, and $found.
Specifically, $found causes problems for me, specifically with the WPML plugin.
$found should be set by the ObjectCache plugin. WPML (and other plugins I would assume), test this variable to see if the lookup value was actually found in the cache. Usually, if $found is false, this means the expensive query is done, and the result is stored in the cache.
Currently, $found is always false, which means the query is done all the time and performance is eroded.
I think setting $found properly when the Object Cache is being used, would increase performance when the W3TC Object cache is being used.