Window borders are very thin (1px) since ubuntu 11.10. So here is how to make borders clickable again. I use the Radiance theme, so the file to edit is /usr/share/themes/Radiance/metacity-1/metacity-theme-1.xml. There you have the values left_width, right_width and bottom_height all with the value 1. Just edit the value to let’s say 3px to make it clickable in higher resolutions. After changing the file you have to relogin.