I think your comparison to 10 inch netbooks is spot on-granted, the Surface is 10.6, but considering I always felt uber crampted on a 10.1 inch netbook, I don't see the utility in having a tablet version of one. As a tablet, I think Surface has a lot going for it (kickstand, snapping apps side by side, flash, file system access), but there's no way I'd use a device that small as a primary computing device for productivity (programming or Office type stuff). Otherwise, its just an expensive VPN client.
It's important to keep in mind that the Metro apps work better on smaller screens than normal desktop apps. They hide a lot of the UI when you don't need it, so there's much more room for actual content. I wouldn't want to run, say, IntelliJ Idea on a Surface, but for many other apps, the screen size is not much of an issue. Also, you can dock the Surface when you're on a desktop, and use a larger screen.
