During the weekend I caught a bit of time and had fun with Autodesk SketchBook. I use it for some time because my tablet is acting weird in Photoshop. First, I had a problem with animated splash, double clicks and couple of other things. I found solution on forums for it. I updated my driver and nothing changed, then I basically turned off everything in pen & tablet and wacom preferences menu, but three or two second lagging in PS still remained. Here are some links that can help you if you have problems with your tablet. Maybe it will work for you.
SketchBook is getting better and better, and there is no lagging at all, It's working nice and smooth, like every serious graphic software should. I even made some brushes of my own and tested them on this image, although, because of final touch, some effects, blending modes, etc. I had to go back to PS.