Explain this shit to me, because I really don't get the appeal of the 7" format. It's basically a large phone, except you can't use it to phone. It's portable, which is cool to some extent, but you're also carrying a phone in another pocket, along with a wallet. Personally I'd go with a 10" android, probably a TF700 + keyboard, or maybe wait out the Nexus 10 or whatever it's going to be called, assuming it has SD or micro SD slots.
History generally isn't kind on early adopters of MS goods. I'd wait out the first service pack on the OS, and probably the next gen tablet, too.