I had a very weird dream about Surface last night, that it was some huge 20-inch-or-so tablet, and that I truly loved it. But, even in my dream, I couldn't do much with it apart from show people the desktop (Metro/Windows style UI wasn't in my dream), and run a web browser.
Anyway, Microsoft have revealed the the exact storage a consumer would receive with the Surface tablet once its in your hands. This accounts for binary conversion, recovery partition, and the software itself. The 32GB Surface will have 16GB of free space, while the 64GB model will have 46GB of free space on-board.
But, you can use microSD cards and USB storage for your external storage needs, which helps in magnitudes you could only iWish on the iPad.