While I agree that CS is useful, its' application is rather limited. Personally, I think it can help with the understanding of phonics and lipreading; I think CS is the reason why I have some understanding of phonics. I also must admit that I never really mastered phonics.
I do not think CS is the reason why I've good English skills though. I already had that before I started on CS. I should have had serious language delays given my background; I didn't wear a hearing aid till i was 2 1/2 years old. My mother says I didn't talk till I was 3 years old. My mother says my first word was Mama only it came out Umma. I have dim memories of my speech teacher teaching me how to say ball to her when I was three but I have no memory of using CS before 2nd grade.
I must confess everytime I see one of these cued speech threads, I feel like rolling my eyes. I don't hate CS. I just think it's limited in its' applications. Cloggy thinks it's because we feel threatened. Hah. It's highly unlikely it'll replace ASL as some ASLers use cued speech as well.