Is define(enable_cache, true) not working in 2.5?

On 2.33 i had define(‘ENABLE_CACHE’, true) in my wpconfig and was able to use the buiilt-in cache quite effectively to store my sidebars.
But in 2.5, nothing happens – nothing is being cached. (I can tell becuase I measure load times by comparing microtimes.)

Also, the cache folder isn’t being populated with anything. Does 2.5 with built-in cache enabled use /wp-content/cache/ at all? Or is it someplace else that I need to create the cache folder?

THanks