Update 4/23/2013: down grading didn't do much nor usb 3 idea. I went and installed the latest driver and... I think I'm going to stick with it.
I was frustrated with pressure sensitivity going out of wack when I'm using photoshop. Basically, when I'm using paint brush in PS I get a line or dot with no pressure sensitivity... it's very random and frequent. I did a lot of tweaking in the wacom tablet properties but didn't do much. I searched around the forums and found some helpful information so tried it and seems to be working okay but still has problems. People suggested down grading the driver. I'm currently using 6.3.4-3 driver. However, that didn't solve the issue like I hoped, so I started updating drivers for usb and other hardware for my pc... than I thought what if I plug usb for cintiq to usb 2.0 instead of 3.0.... That's when I started noticing difference... I think. Seems like I'm getting much less sensitivity issue now than before.
I'm using Cintiq 21ux with 6.3.4-3 driver.