This post is retained for historical purposes. The problem described here was fixed by Apple with the 10.9.2 release. If you're experiencing this crash, please upgrade your OS.
Many MacBook Pro models have two graphics cards (GPUs). The “integrated” GPU uses less electricity, and has sufficient performance to run the built-in screen for normal tasks. The “discrete” GPU has much higher performance, but uses more energy.
Mac OS X switches between these two cards dynamically when it determines that there is a need for the higher performance of the discrete GPU. For example, the discrete GPU is used if you plug in an external monitor. It is also often used when applications capture video of what’s currently on the screen.
The most recent version of Mavericks, 10.9.1, introduced a graphics card driver problem which causes WindowServer to crash when doing some video tasks using the discrete GPU. When WindowServer crashes, you are immediately logged out. It can appear that your machine has “instantly restarted” and you have to log in again.
If you are seeing WindowServer crash when using Skype or any other application for video calls or for screen sharing on your MacBook Pro, here is a workaround which you can use to reduce or eliminate the crashes.