Macbook Air short Battery Life
If you're not using a lot of power, this isn't normal. On http://www.apple.com/macbookair/features.html#battery it says up to 7 hours, clearly implying that you could get less. The footnote as text as follows:


  The wireless web test measures battery life by wirelessly browsing 25
  popular websites with display brightness set to 50%. The standby test
  measures battery life by allowing a system, connected to a wireless
  network, to enter standby mode with Safari and Mail applications
  launched and all system settings left at default. Battery life varies
  by use and configuration.


So, if you had all of the the brightness on max, CPU topped out, GPU working and storage downloading, I would expect the battery to last between 2 and 3 hours, so you may have a perfectly normal battery or there may be an issue. This sort of thing is exactly what the Genius bar and AppleCare exist to answer on a case by case basis if the online tips don't work or you want to seek a professional opinion and possible repair.