Playbill has news of a musical adaptation of Matilda for the RSC:
Roald Dahl’s popular 1988 children’s story Matilda will be adapted into a new musical. Tony-winning director Matthew Warchus will stage the production for the Royal Shakespeare Company, which will premiere at Stratford-upon-Avon’s Courtyard Theatre in winter 2010. The show will feature a book by playwright Dennis Kelly… and music and lyrics by Australian comedian, actor and musician Tim Minchin.
I suppose this could be interesting, depending on how the book and score turn out. Matilda is not one of the Dahl books I know well; in fact, I’ve never read it and only know the story from the film.
Musical Cyberspace 
I’ve always loved the book, and was terribly, terribly disappointed in the movie. If I remember correctly, it was set in the US, and the entire reason for Matilda’s powers was different, which ruins the point of the book. Also, the parent’s had inexplicably changes physical appearance, which seemed dumb.