Hmmm not sure Barry. I have CS4 and really use the B+W layer alot. Its great and non-destructive on the original image.
It was the biggest reason for me to move from 3 to 4 at the time.
CS5 is new so many people won’t have had the chance to use it yet. By all accounts so far it seems great.
Personally I’m going to hang on a while before I upgrade.