I just read about the Macbook Air and after I read about the Slate thought “Why would I want a Slate?”.
Good question. Suppose what you really want is access to Win7 as well as OS-X?
Get a Macbook Air with 4GB RAM and 128GB SSD, and VMware Fusion, and run Win7 in a VM -- best of both worlds for less than the cost of both separately.
Or skip the VMware, and BootCamp the SSD. Now with OSX 10.6, the BootCamp drivers for Win7 permit reading the OS-X partition from Windows (and vice versa as before) which is really handy.