I know this is an old thread, but I think that the below information is relevant to those with the same question that mydoghasworms had a few years ago.
Wacom support is not really up to scratch in 15.04. Still, you can buy a Wacom tablet knowing that you can get it to work well, though it will take a bit of work. I use a combination of the Wacom Tablet settings in System Settings and xsetwacom to set the buttons on my Intuos4 and Intuos5 to things like hotkeys, modifier keys and toggles (even the ring toggle button works). I have not managed to get the LED displays to work, but I didn't try very hard and others seem to have managed it, and in my opinion, a tablet without those working can still be a killer tablet.
These links will provide very useful information:
This one specifically for the correct numbers of the buttons in xsetwacom, that took me ages to figure out:
Personally, I think Ubuntu really has to put a lot more effort into the Wacom tablet setup and configuration tools, but still, get yourself a tablet, it is worth it!
By the way, KDE used to have even more customizability options, including the ability to easily switch between program specific button setups, so you could have a setup for Gimp, and another for Krita for instance. This was great, but those options seem to be gone or not working in Plasma 5.