Some of the decisions that went into the Surface just don't make sense from a user experience point of view.
The stylus has a click button which is cool until you realise it only opens OneNote and you can't change that - unless you want to start messing round with reg edits. The dock has a magnet to hold the pen until you realise it's only on the left hand side and inconvenient for right handed users.
The on screen keyboard has a poor layout, click areas on screen are far too small for finger touch and takes repeated touches. It's awkward to switch between physical keyboard and touch screen to the point that neither feel natural.
The Surface itself gets quite hot under the kickstand and doesn't seem to dissipate heat well enough. Out of a number I have used quite a few had the BSOD out of the box. The battery compartment in the pen is shoddily made so that the spring often touches the metal body shorts out and makes the pen dangerously hot. Oh and the pen takes 2 batteries - one for the stylus and one watch battery for the button - neither of which are rechargeable.
Not sure if windows 10 will make them any better from an OS point of view but overall they are a good idea in theory but very awkward in practise.