I've never had much use for multiple desktops, but I suppose it could serve as a poor man's multimonitor substitute. I might even use it that way.
No love lost for the charms bar on the desktop. Search and share are a good idea but it's so underutilised, ugh. It's still a great shortcut on touch devices though. Especially on touch tables which often lack a physical Windows button.
What I would like to see: a way to toggle it on or off based on how you're using your convertible. I have a Dell XPS12 for work, and I'd love to see the charms bar disappear when I'm using it as a laptop, but become available again as soon as I flip the screen back and use the device in tablet mode.