If you have a Windows8 tablet then you definitely want to install the FOSS app MyPaint:
http://mypaint.intilinux.com/?page_id=6
It has been smooth as butter on my old Asus ep-121 and has been really the only app I keep coming back to use the tablet for. Unfortunately, the latest 1.1 version is still Linux only, but will arrive eventually. It will really help the workflow with onscreen panning/rotation, which is the biggest hindrance on a tablet with the 1.0 version.
Pressure sensitivity is fine with Mypaint, as I had installed the Wacom driver, but unfortunately the Wacom calibration tool is only 4 point and is slightly off compared to the inbuilt Windows one. I would rather have the calibration slightly off (mainly as you get towards the edges) than have no pressure sensitivity. Krita is the other FOSS app that is growing in leaps and bounds and has the Mypaint brush engine builtin. Can see it eventually being a full Photoshop replacement for studios with its Linux support and OpenColorIO capabilities.
Hopefully with Wacom working on their own tablet, they will get their driver/calibration act together and this will have a nice ripple on effect to all the other Win tablet makers!