I just ordered 8 more on Monday. That'll put me at 12 in this system. I couldn't pass up 8GB of DDR3 1600 for 50 bucks. I OCCASIONALLY use up all 4 I have now, but I don't do a whole ton of actual work on this computer.
Main: i7 4790K - Z97 mATX - 16GiB DDR3 1866 - GTX 970 - 256GB 850 PRO - 500GB 840 EVO - HGST 3TB - U2415 - Win8.1 Pro x64
Work/Play: 2015 13" rMBP
Work: 2014 Dell Inspiron 7000