Guy at work just bought one....it's two weeks and 100mi old. It started overheating, and now is back at the dealer waiting on a water pump impeller. Quick scan of the forums seems it's not uncommon.
Not a knock against KTM, they make incredible bikes (I need a KTM motored Husky 501 in the WORST way!) but maybe the 390 needs to work out a few kinks first....