I am using Windows 7 64-bit. But this would probably also apply to 32-bit users. My tablet is a Wacom Bamboo Pen and Touch. But, again, this would probably apply to all other Pen Tablet products, even those not made by Wacom.
I've had issues with delays when clicking with my pen. Whenever I left-click anywhere on the screen with the tip of the pen and trying to drag, there was always a half-second delay before the pen performs the correct action. This was especially annoying when trying to paint in Photoshop or sculpting a 3d model in Mudbox or just performing any click-and-drag action in general.
I have asked about this issue sometime ago.