I try to keepp shots within 30 yards but a deer at 35 is just as likely to get stuck. I am confident I can hit my mark out to 40 but a lot can go wrong at that distance. The two main reasons I limit myselt to around 30 yards is a living deer will likely not stay still and give you the shot a target will. You have to find your mark and put the arrow there before the animal takes a step or jumps the string. 1 step means the diffrence between a quick kill and agonizing long and sometimes unsucessful tracking job. If you've ever lost one you know what I mean![:'(]
The second is terraine features. Most of my bow hunting setups are in fairly heavy cover. I have a few lanes I can shoot through out 35 or 40 yds but for the most part the animals that pass will be within 30 yards. This is how I pick a location to hunt and I do so with shooting situations in mind.