Like Bam says painting isn't considered good practice anymore, though various paints and tars have been used in the past. I certain species internal decay in the trunk is actually beneficial in helping to reduce weight and strain in the bole. It can give the tree a certain flexibility that helps it take the strain of stresses caused by high winds that would snap a solid tree.
In various religions and myths it's considered the tree of death, associated with graveyards, poisoning and arrows. Some woodworking books do say that you can use it for food utensils but especially if it's something you'd use a fair bit I'd avoid it.
Used to have this fantastic old chap who came to the estate periodically, he worked for a veneer company in southern England, he was fantastic, could take a cursory glance at a tree and tell you it's life story; if it had suffered from drought, disease, lightning, fungus. (I was dubious first time I met him till we took a couple down and exactly where he said there would be damage (hidden way inside the tree with no obvious external sign to the rest of us) there it was. Then again he paid top dollar for certain woods and just didn't make mistakes.
