Have the memory of my Mac mini i5 (build 09/2011) upgraded from 2x1GB 2x4GB on now. The exchange was smooth, boots without problems, full memory is recognized by the system (OS X Lion). The mini is running as a media server permanently in 24/7 operation and shows no dropouts. I can subjectively recognize some felt better access times, but I had an even one day in the base assembly run mini on.