Ok, since this thread was started by my friend Ayin I'll chime in...
I too do not know of the flat cap controversy. First, as a piper, I can assure many pipers even from Scotland/Ireland shed their glengarrys after competing and put on their flat caps with their kilt. Don't argue, I have pictures. My personal opinion is that I dislike glengarrys (piss cutters) and always have. We have to admit as pipers we wear some pretty silly looking headwear sometimes. I like the look of flat caps better than some of the balmorals and bonnets I've seen.
Secondly, how can anyone state an arguement about flat caps when alot on this forum are wearing their utility kilts with tennis shoes, baseball cap? Or, some have the Dropkick Murphy look. I've seen Ayin and the Sonoran Scotsmen and they look great.