Interesting how this thread has evolved into a discussion on what does or does not constitute cheating.
Personally, as long as my opponenent(s) are calling lines fairly (which is the case 95% of the time), I'm a happy camper. Most everything else is like water on a duck's back to me. People, rec tennis is supposed to be fun, not a source of stress.
I'm not put off if my opponents warn each other after putting up a short ball. On the other hand, I don't do it myself, because I find it pretty useless.