I had this exact problem too - my q, w, e, r, t, y, u, i and o keys didnt work. (only these keys were affected) MBA 2011, 13". Try pressing the "alt" (option) key whilst pressing the unresponsive keys a number of time. That seemed to work for a while. Also, I found the problem is much worse typing on my lap. If I put the mba on a flat surface, it seems to work much better. Randomly, previously I've found that tilting the laptop brings it back to life. Obviously not much of a long term fix.