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:
<cache>
If this next line was not commented out, it was going to be saved to memcached and NOT the file system
<!-- backend>memcached</backend -->
<slow_backend>Apc</slow_backend>
<slow_backend_store_data></slow_backend_store_data>
<auto_refresh_fast_cache></auto_refresh_fast_cache>
<memcached>
<servers>
<server>
<host><![CDATA[localhost]]></host>
<port><![CDATA[11211]]></port>
<persistent><![CDATA[1]]></persistent>
</server>
</servers>
<compression><![CDATA[0]]></compression>
<cache_dir><![CDATA[0]]></cache_dir>
<hashed_directory_level><![CDATA[]]></hashed_directory_level>
<hashed_directory_umask><![CDATA[]]></hashed_directory_umask>
<file_name_prefix><![CDATA[]]></file_name_prefix>
</memcached>
</cache>