I struggled with an issue that bugged me for a few hours. I noticed that var/cache was empty! That was strange..so I did some research and this happened right after I setup apc and memcached.
It turns out the the instructions i followed was saving them into memcached instead of the file system under var/cache
Here is what my app/etc/local.xml looked like:
If this next line was not commented out, it was going to be saved to memcached and NOT the file system
<!-- backend>memcached</backend -->