The first problem is speed. Everything you do on the Surface takes more time than you expect. When you load an app, switch between apps, launch a Web page, go back to a previous Web page, check your email, and do pretty much anything else, you’ll find yourself waiting a half-second too long. This sounds like nothing, but when you compound that time time across every action on the Surface, the wasted half-seconds add up to an annoying trudge.
Only a decade ago, Windows XP was snappy and Mac OS X was the one where things like resizing windows or even pulling down menus felt slow.
I think this is a serious problem for Microsoft, though, because responsiveness is much more important on touchscreen UIs than desktop UIs.