Energy Saver settings!
Further to the the var. & sundry quirks with this mid-2011 MBA 13" ... I read about changing the Energy Saver settings and simply moved the slider to 'Never' for the computer and unchecked 'Put hard disk(s) to sleep when possible'. No more freezes, no problems waking from sleep (well, it doesn't) and after repeated 'Repairs' (Apple's own, DiskWarrior, Drive Genius) the USB connected items properly show up, e.g. a CF card in a reader or inside the camera. - Someone here explained (PC user), well, there's maintenance going on and if going to sleep happens during such a 'house keeping' task, things drop into an unending loop and one has to force a shut down and restart. I understand too little of these matters, all I can see is the result of suppressing the computer's going to sleep. As it has solid storage, not a spinning hard drive, this seems of little consequence (does not seem any warmer than observed before).