It's heavier and thicker than a dedicated tablet, and the weight isn't as evenly distributed as it would be in a tablet. Convertibles must compromise between the power of a laptop and convenience of a tablet, and this machine makes very few compromises as a laptop (2.8ghz i7 cpu, 8Gb RAM, 140Gb solid state drive, etc). The surface pro's design looks to be weighted the other way, with more of an eye towards tablet functionality than laptop functionality (I suspect it'll be difficult to use in your lap, for example).
But the Lenovo X220T is one heck of a machine, and even though it's a bit clumsy in tablet mode, using it in tablet mode convinced me early on that Win 8 was a great tablet OS, much better than iOS or Android in that role - if it gets the apps.