Understandable... they don't want anybody posting screenshots of work in progress without "forcing" them to show it's work in progress - the email to early adopters mentions that you should make it very clear that this is probably a pre-alpha image.

I had a go at it (thanks sledges) and the watermark really doesn't intrude so much ;-)

EDIT: FWIW, I've already seen somebody mentioned this as a RC, and it isn't a RC.