Battery life on a core i7 Macbook Air
I have the same Air as you and I am getting 5-6 hours. So not to much off of what the advertised amount is. Your battery sounds faulty to me.

The last computer I had had a faulty battery. It was replaced for free and within a couple of days. Back then they simply replaced the battery on the MB because it was removable. Chances are now they will give you a new laptop because the battery on the Air is harder to remove. You might be without a computer for a few days though. I don't know what they do in other countries, but in Spain they just took it and mailed it to Holland to get fixed and then mailed it back.