I have just added APO. If I examine the headers on my own site using Chrome tools, I see the cache HIT.
I ran some speed tests with Pingdom to compare before and after speeds but wasn’t seeing any changes in the results at all. After a bit of digging, I noticed the cache status was showing as DYNAMIC in the Pingdom test results.
I also looked at a few other sites that have enabled APO (found them in the community forums here) and tested them in the same way. Same thing. I see HIT when I examine the site directly, but run those sites through Pingdom and it misses.
This gives the impression that APO isn’t providing any benefits. I’m sure I can’t be the only one trying to confirm results using Pingdom’s test tool so it would be good if this worked.