I've been experiencing some extreme UI lag when sublime (1.3) is running on a vertically oriented monitor in windowed mode. Keyboard and mouse actions are choppy and delayed about one second, menus are slow to draw, etc. Actions such as find in project do not seem to be affected. I have tried toggling different combinations of controls (minimap, tabs, toolbar) and views (single, double pane, etc) with no impact. Fullscreen mode works normally, it is just windowed mode that seems to have a problem. CPU usage shoots up to about 50% (up from 0) and the mouse lag continues for several seconds after the sublime window loses focus.
I have experienced this on two seperate machines, a 1.8Ghz core2 with 3GB memory & an ATI Radeon X1300 (work machine) w/ dx 9.0c running XP, and a 3ghz core2 w/ 4GB & NVidia 9800GX2 dx10 running Vista (home machine). Both experience the same issue (lag in windowed mode, fine in fullscreen mode).