Birnbaum's is just fine, it's bright & fun and is neat for the family to get together to do some Disney dreamin'. However, I think it's a little too "fluffy". In other words, I don't think it thoroughly addresses issues that first time Disneyers (crowd shock, weather shock, $$$ shock) may face. For REAL information this board is the BEST source of info. I have just taken my fifteenth trip to WDW and consider myself a well informed Disneyer, but I always find new and helpful info right here.
I've heard some people say they like the "Unofficial Guide" better, although I cannot recommend it because I've never read it.
Good luck, happy planning, have a tiggeriffic trip!!