[rayiner]

This is almost certainly the right answer. Synchronization/priority is the #1 culprit when people complain that a UI is "laggy." It was why BeOS was so renowned for being snappy--all rendering was done in a separate high-priority thread. It's also one of the reasons Linux has always been criticized for a laggy UI: the X server/application/window manager triumvirate isn't so much slow as it is a total mess from a priority point of view. You end up needing priority-shifting schemes UNIX doesn't have (quickly shifting priority from the WM to the app to the X server as an event flows from the X server through the WM to the app).