I'm not sure how I feel about Old Tom Bombadil. I think it's a great song, but not sure it really fits the carefree and cheerful nature of his character.

EDIT:
I just listened to the Reprise of this song, sung by the actors who actually play Tom and The Stranger (aka Blue Wizard 1) in the show. This is much better in style, with a lilt and bounce that is right on. Rufus's version will likely be used for closing credits.