If it's something I'm capable of doing myself, then I'll do it. This includes changing oil & filter, inspecting (and changing if necessary) the spark plug, cleaning and re-oiling the air filter, changing front/rear differential fluid, etc, etc. No need in paying someone else to do something I can do myself.
I've also done a few things that were a little more demanding. Recently I put a new ball joint in the front suspension of my '00 Foreman and regreased the other three (using a turkey marinade injector syringe converted into a mini grease gun). Also, about 5 years ago I replaced the front drum brakes with disc brakes, which was probably the best thing I ever did to the Foreman.