Spilled a small amount of water on my keyboard and shorted the power button. Since this would have cost me over $400 to have repaired at a shop, I bought the top case on eBay for $125 (new) and the 54 bit driver kit and spudger.
I followed the take a part guide before ordering to make sure I was comfortable doing this and all went well. Ordered the top case, waited two weeks (came from China) and finished the job in about an hour. My MBA started right away and has be problem free since.
As I was not sure what was broken, I did have to spend $90 to have it trouble shot. Since I was still saving a significant amount, I went ahead and did the job myself. I am not afraid to open my tech fix what I can. In the past I have replaced iPhone 3 glass, iPhone 3GS home button and now a top case. I might want to work at an Apple Store now ;-).