Lion works great on my 2012 MBA.
I keep hearing everyone keep yapping that we all should run Mountain Lion.
I looked at ML's list of new features and almost all of them appear to deal with iCloud and better integration with iDevices.
Since I don't use iCloud, and have no iDevices, the upgrade would not yield me any results.
IMO, if Lion works and you have no need for iDevice integration, ML seems un-needed.