How can I rename desktops in Mission Control? The default new desktop space is named 'Desktop 1'. If you create a new one, it is named 'Desktop 2'. Is there a way to change those default names to something more meaningful?

Additionally, it looks like you can't rearrange spaces either and the 'automatically rearrange spaces based on most recent use' checkbox seems to do nothing.
No, there is no way to do that in the current build. Well, sort of. An example is if you have iTunes open in fullscreen in a separate desktop, and go to mission control, the desktop will be called iTunes.