Retina MBP and 2219 nightly.
I know, I was trying to toggle it to see if there is a difference.
Video showing typing lag: http://dl.dropbox.com/u/18933210/gpu_window_buffer_lag.mov.
When I decided to redo the video and remove my project name from it - I wasn't able to reproduce the lag.
So it only happens when I have large Rails project opened in the sidebar (there is a project opened in the video, I just cropped it).
When I close all projects, or open small one (e.g few flies only) – there is no lag.