Just dropped by the Microsoft Store at Yorkdale Mall today to check out the SP3. And wow, am I impressed. The keyboard is much better than I could have imagined, I even tried it out in my lap and it was excellent - it's not as good as a full-on laptop, but it's plenty good enough. Even the trackpad was solid, and there are very few trackpads I've ever found bearable. The pen is also wonderful, and I was unable to replicate the issue in which your palm accidentally triggers the Home button - maybe they've patched this out by now?
As far as using it in tablet mode, it's quite good - I have no beef with the abnormally large 12-inch size, it's still perfectly usable IMHO. However, I can't see myself holding it up for an extended period of time. 800 grams still makes for a hefty tablet, though it's light enough that you won't feel the weight over short periods of time.
I only had two minor concerns. One, I couldn't get the virtual keyboard to appear in the Modern version of Internet Explorer (and other Modern apps) no matter what I did. Mind you, I have very little experience with Windows 8, so maybe I'm missing some kind of trick to it? Or is this just a bug?
My other concern was that the pen seemed to disconnect on me randomly at one point. I had to hit the top button to trigger OneNote to get it working again - perhaps there's some issue maintaining connectivity that needs patching? I think I've heard of this issue in one of the reviews I've read, so I'd hope that Microsoft is aware of it.
I wanted to give the gaming performance a test by sneaking in an installation of League of Legends, but it prompted me for an admin password when the installer ran - guess I'll have to wait for my preorder to arrive before I give that a try!