In cs5 the masks panel was introduced to encourage the use of non-destructive lyre masks. It was a handy place to view all masks andcrevisitvforvrevision of refine mask command.
It appears to be totally gone. Is that the case? Why?
It's still the masks panel in CS5.
In CS6 it's part of the properties panel.
And may I mention that I think it’s terrific you are offering a public beta of Photoshop CS6?