I've been wary of doing a clean ML installation, but in the last couple of days my 2011 Air would not wake up from sleep a couple of times (having to hold the power button to reboot), and I had enough: time to do a clean install. Considering you are already backed up with Time Machine, the process is fairly simple: press CMD+R while your system is booting, use the disk manager to erase your drive, and then choose the internet installation. Now I have a clean system without all the stuff that I've been collecting through all these months and that may have been affecting battery life (growl, serviio, third party drivers for stuff I don't use anymore, etc.). And a clean OS installation. So far the issues that seem to be fixed with my shiny new OS: - Immediate wake up from sleep (before it would take around 5s) - Improved battery life (now I get around 6h to 7h estimated battery life where before I would get around 4h). - Random freezes crashes gone. - Non waking up from sleep gone. - Improved free space (before I got around 20GB free and now I have 40GB, although this is also because with a new install you can skip reinstalling stuff you don't use anymore). - Improved responsiveness, the system feels "snappier" in general. - Safari also feels snappier while browsing. So guys, my advice is that if you have some of those common issues and you upgraded to ML from Lion, give a clean install a go.