Your situation is very similar to mine. My brother is the addict (he is 37) and my mother is his enabler. I'm 39, by the way.
I, too, get mad at my mother because of all this. It has been going on for YEARS and both of them just keep getting worse. I've given her books on codependency to read too. The first time she just gave them right back! This time she has kept them but I don't think she has read them.
I don't really have much involvement with my brother and have absolutely no involvement as far as helping him out with his addiction. My mother gives him all the 'help' he needs. I think that if my mom were to (God forbid!) die tomorrow I may never have any more contact with him at all.
His being an addict has really ruined the relationship my mother and I once had as well as the relationship she has with my children, her grandchildren. She is so wrapped up in my brother and his addictions she barely has time for anything else, even herself.
I've been trying for years to get someone to do something about it, but for now I'm just trying detaching from the whole situation to save my family's sanity. Maybe they won't do anything about his addictions, but I can do something about how I deal with them.
I know where you're coming from, I'm right there with you.
Good Luck!