My driver side window had the exact issues described by Moncha and various other members. The window seemed to have a slight forward tilt, and upon closing, would get stuck tilting backwards. I looked at Moncha's fix and followed his advice, but it wasn't enough in my case. The window rail (the center lift where the cable is) appered to have a little play allowing for a slight tilt when going up and down.

My fix was quick and easy, I removed the window and braced it up. I took a drill and bit and started drilling/cutting upwards on the bracket hole on the right side. Be careful not to drill through the door :-)

Upon re-installing the window I made sure that the bracket would now fit as high up in the extended hole as possible, tilting window tight to the left. Tighten down and voila. It goes as smooth as it should be and I can't wait 'till the passenger side starts screwing up.
Pics available upon request.