The intuos5 S is very portable. Its the ideal size between mobility and usability for my needs.
While the intuos5 small looks very nice, the build quality is not on the level of the intuos3 series. Especially the grip pen's build quality. It's a subtle thing but you can tell it.
The pressure-sensitive drawing expience is typically Wacom. Good. The pen surface is my biggest concern. It feels nice, but time will tell if the pen-nibs will survive.
The level of app specific customisation options is also nice. Out of the box comes a decent Photoshop experience. There's one thing about the buttons. You better press one at a time and assign key combos to them since it's not easy to press 2 at a time (Zbrush!) But it's not a big deal. If cleverly customized, Zbrush is much more fun to use with this tablet. (I assign ctrl-LMB to the eraser tip for example)
Having moved from intuos3 to 5, I was very impressed by how good wacom became in customisability. And TOUCH is not a gimmick, it's actually very usable. I'm on OSX here btw.
My biggest motivation for buying the i5s was portability but I was surprised by many good things that came along too. There's also the opotion to go wireless if you buy the wireless kit
That's it. Hope it helps some people make safer decisions.