I do it all the time...................I'm still under that umbrella of a 3 year 36000 warranty though. (as long as they dont check my computer. if they do, the warranty is long gone lol)
I do it when I feel like it, which is often, mostly when Im showing off my exhaust. Although, I think its a bad idea.
The exhaust (ANY exhaust) sounds FAR better under load. You're just shortening the life of your engine.