Today I reloaded OS X Lion on my old 11" MacBook Air 2011 with 2 GB of RAM. Did Lion as that is the version that the Web Installer allowed me to install. I have applied all the available updates and the apps that I want it to have. In fact using it to type this post. This Mac has not performed this well in a long time. No spinning Beach Balls at all since it completed the reinstall. And the fan has not spun up to high speed at all. Feels like a new machine again. I do not know if the performance issues it was having were due to having had multiple OS upgrades over the last 4 years, or just basic OS performance degradation over time. I plan on giving it to my wife and she will only use it for web, email and occasionally for MS Office. My wife is easily frustrated and short tempered with technology. If it has any performance issues, she will constantly complain. Her current Windows Laptop is a major source of frustration to her as it was cheap and under powered when she bought it. Since I converted her from Android to iPhone, she has been happy with her phone and not complained at all. So I am hoping the conversion to OS X will have similar results. Just do not want to handicap the conversion by installing a newer OS if it will cause this MBA to slow down again. So, any major reason I need to upgrade to a newer version of OS X? Any major security bug in Lion that I need to be concerned with that would force me to go ahead and upgrade to Yosemite again? I am just concerned that the performance issues I had were related to running Yosemite on 2 GB of RAM.