For me it would really depend on the entire situation. I know guys that shoot more than their share, always have and probably always will. I don't condone it or hunt with them...but if they want to play that game and take the chance, that is their deal. I don't really consider them "friends" in the true aspect of a friend....but at the same time I have way more important things to worry about than turning them in. If you do decide to turn them in....you had better do it anonymously. Some people are nuts, and dealing with that certainly isn't worth it - not over a deer.
Don't get me wrong...some folks certainly need to have the law called on them and they deserve it. Heck, some folks deserve the slammer for a long time for the crap they do....and some folks, well IMO its just not that big ofa deal - not big enough for me to get involved. The guys I know....they don't road hunt, they don't trespass (only hunt their own land), and they don't hunt out of season. They just don't tag all their deer, and usually shoot an extra buck or two each season.
I have called the law before a few times....just pick your battles wisely is all I'm sayin.