I just upgraded from Kubuntu 11.10 to 12.04 and install Krita 2.4.
Problem is my Wacom Bamboo Pen (CTL-470) works but with no pressure sensivity at all.
Still, it works flawlessly in GIMP 2.8 and MyPaint 1.0 in the same time.

Could you please tell me how to fix this?

We seem to get a new post like this pretty much on the release of every new version of Ubuntu. Every other time it has been because the Ubuntu dev's did something that broke tablet support in QT, and people needed to file a bug onm Launchpad and wait for them to fix it.

I was really hoping they wouldn't break it again this time around...

Note: This is why you'll see my username is Kubuntiac, but my OS is Chakra. I love Kubuntu overall and used it exclusively for years, but then I needed a KDE based distro where tablet support didn't keep being broken and the bug disregarded because it didn't affect GTK apps.

Here Intuos 3 and Cintiq ( Int3 generation ) works fine on Kubuntu.
Wacom Bamboo Connect CTL-470/k and Pen & Touch CTH670 are just newer model. I guess they work with the driver ( thats why you have Mypaint and Gimp ok ) but not yet with Qt apps ( Krita ).

Thank you for all your advise.
I reinstalled the Kubuntu 11.10 and upgrade to 12.04 again and Krita can now detect my pressure just fine.
I still don't know how and why it happens but the problem is solved.