I also tend to write when I have received good service. I recently had cause to write to GB Airways concerning the standard of the food served on board - yes, good airline food.
The response seemed to me to be one of incredulity. Obviously they don't receive many such compliments!!
So each time we receive good service let's send an e-mail thanks or congratulation card - airlines deserve compliments sometimes and obviously revel in receiving them instead of the eternal complaints they must receive.