so this might be why it's not working (if it isn't) at all, or at least seems like it's not working with the apc.php that comes with APC (as installing it like I did, I didn't get it, I had to extract it from the package and then upload it) but all I'm seeing is:
1 Hit 0 Misses
System Cache Entries shows nothing for Script Filename, nothing for Hits, Size 656 and surprisingly it's saying it was last accessed AND created at: 1970/01/01 00:00:00 and then last modified was at 2pm today?
Per-directory resources has nothing for directory, 35 filenames, 0 hits, 421264 for size
NOW, I also have a apc2.php which is just:
and that shows:
[nslots] => 4099
[ttl] => 7200
[nhits] => 1208
[nmisses] => 233
[ninserts] => 53
[nentries] => 35
[nexpunges] => 0
[stime] => 1382663331
[mem_size] => 421264
[file_upload_progress] => 1
[memory_type] => mmap
[cache_list] => Array
and then lists a bunch of WP/W3TC related items
I'm pretty sure APC is actually "working" as in caching, but any particular reason for the discrepancies there?
Final question, is there anyway (outside of varnish simply inserting the header) to tell if varnish is actually caching anything?
I've used a bit more sophisticated form of the same approach NinjaForms posted above. There are tools that allow you to see HTTP headers, and those may provide good tips on what's going on. Live HTTP Headers for Firefox is a free tool.
apc.php was very helpful in determining if the caching was working. I've not used tools beyond that. The 1970's date you see is the Unix Epoch, and I guess something has slightly failed somewhere because it's using the "fallback" value. If it's working, I wouldn't worry about that.