I have a mid 2011 iMac i5 27'' on which I have installed Mountain Lion. Everything is working great, except for one thing. I have my Energy Saver set to the default Sleep of 10 mins of non use. Whenever I was downloading anything under Lion it would always stay awake until the download had finished, even if that was 2 or 3 hours. Since changing to Mountain Lion my iMac sleeps exactly as per Energy Saver settings regardless of the fact that there is network/hard drive activity. Is there a setting somewhere which needs tweaking? I have tried checking/unchecking "Wake for Network Access", but that doesn't make any difference. Any ideas?