I ran across this little audio article on NPR which may be of interest to fans of Tom Waits. Basically, he's not very happy with anyone trying to cash in on his image and I can't really blame him. He's got such a unique delivery/style that when you hire a sound-alike for a guy like Waits, I think he has a valid complaint that it may damage his credibility with his fans.
And while on the topic of using music in ads, I heard a pretty decent web doc on BBC1 on precisely that subject which you may want to check out. They talk about primarily British artists, but there's nothing wrong with that, right?