I have a Wacom Graphire, and I'm working on Linux 64-bit (Ubuntu Natty, to be precise). The version of xserver-xorg-input-wacom is 1:0.10.11-0ubuntu4 and the version of xorg is 1:7.6+4ubuntu3.1.
The problem is that the XInput driver/module sometimes briefly reports (as shown by the xidump tool) the pressure as 0, together with a spurious x-tilt of -900, even though the Graphire has no tilt support, and I am pressing the pen down firmly. It seems to happen mainly when I hold the pen still or move it very slowly, when I move it swiftly it doesn't appear to happen.
The wacdump tool does not show this problem. I have to shut down X to be able to run wacdump, but when I do, the pressure is reported correctly throughout. So it is not likely to be caused by the pen or the tablet itself. Apparently something is going wrong when translating the values for XInput.
Please let me know how I can help debug this problem!