I'd really only complain if this kind of thing is frequently impacting your travel. Last summer, I had three mechanicals in two weeks (DTW-ORD, ATL, and PHL) and after the third one, I wrote a polite letter pointing out the discouraging trend and received 10,000 miles. I was happy I mean if it happens every now and then I figure it's just part of air travel but the frequency was upsetting enough for me to write in.