Tested on a Windows 7 64bit System with a Wacom Bamboo Pen Tablet and Blender 2.62.
All related drivers are updated.

The issue can be reproduced by having at least two windows of the SAME blender instance open at the same time. This can be achieved by using the "Duplicate Area into new Window"-Command. Attempting to use pressure-sensitive brush strokes for any painting or sculpting will only work in the window that was opened last. Every other window will interpret every stroke as being full pressure. Closing the most recently opend window will "re-enable" the previously openend window for pressure sensitivity.

This behaviour does NOT occur between two windows of DIFFERENT blender instances.