This gets discussed every once in a while, here. The most common breaking point seems to be .223 Rem. Some states allow it, many do not. Some folks will use it because they trust themselves to only take shots that will produce an instant kill with that cartridge. Some folks will not shoot a .223 at deer under any circumstances as they feel that the wounding potential is too high even with generally good shot placement.
North of .223, few folks will argue agaisnt any cartridge choice. (Though some folks will argue about ANYTHING.)
South of .223, few folks will argue in favor of any cartridge choice. (Though some folks will argue about ANYTHING.)
Some folks will feel they need to tell you that you could kill a deer with a .22 or a .17 Mach 2, if your shot placement is perfect. But these folks will say the same thing in a "which caliber for mastadon?" thread, so don't mind them -- they can't help themselves.
-Sam