Oh joy of joys - after 10 days away in the Lake District I'm reunited with my workstation and can relegate the PlayBook to light and trivial duties.
As a result I've been able to do a few comparisons. The Core i5 version of the Surface has a 10.6" display, is just over half an inch thick and weighs about 2 lb. The iPad 3 has a very slightly smaller screen at 9.7", albeit one with more pixels so far as I can tell, is just over 1/3rd of an inch thick and weighs about 1.5 lbs. The Lenovo ThinkPad X230t Convertible Tablet has a bigger screen at 12.5" but rather less pixels at 1366x768, is about 1" thick and weighs in at, for a "tablet", a rather portly 3.7 lb. The only reason I've chosen the X230t as an example is that it has a touch screen - if a touch screen isn't needed then there's a ton of ultra-books out there to choose from.
The point? The Surface (Windows Pro version) seems to fall uncomfortably between two stools. It's too big and heavy to be a true tablet but decidedly underweight if it's to be considered a notebook replacement. There's a (not entirely complimentary) review up at Hot Hardware
of the X230t - the review model sported a Core i5-3320M, 4GB DDR3, 320GB HDD and cost $1249 as tested. Compare those specs with what we already know about the Surface and you'll see why I consider the Surface a toy. I'm tempted to suggest that the Surface is for Suckers but that would be undiplomatic.
There'll be some for whom it will work well but I'm firmly of the opinion that something the size of the Galaxy Tab (or a PlayBook if you already own a BlackBerry phone) is far better if portability is the priority. But if you want to do serious work then the Surface will frustrate and one would be far better off with an ultra-book. And if you must have a touch screen/stylus input then get an X230t or equivalent...