While the gfxstatuscard tool works in prinicpal (reports and can keep you on Intel integrated graphics), the discreet NVIDIA GPU is fired up anytime an external display is plugged in which effectively locks me down to just using the internal display. This is effectively a deal-breaker for me, so I'm packing my bags and downgrading to Mountain Lion. 10.5 good, 10.6 good, 10.7 lemon, 10.8 good, 10.9 lemon. Lets hope the next one Apple makes is OS X Lemonade.
Problem:
WindowServer enters an uninterruptable wait state on OS X 10.9 and up when using the NVIDIA graphics. Often occurs using conference software, Skype (http://community.skype.com/t5/Mac/System-hang-on-Mavericks-when-screen-sharing/t d-p/2352707) or GoToMeeting (http://support.citrixonline.com/en_US/GoToMeeting/knowledge_articles/000138065?t itle=Mac+10.9+Crashes+When+Using+GoToMeeting%2C+GoToWebinar+and+GoToTraining). Can occur outside of these apps as well, but seems to easiest to trigger this problem. Not sure if Hangouts is affected, but hangouts uses a billion percent CPU, so who knows.
Symptoms:
Mouse moves on screen, screen does not move or refresh. Date and time are stuck. Mac appears responsive, caps lock lights and illuminates. Any apps that are open are still functioning (i.e. Pandora still streaming, Spotify still playing, audio call in progress) but everything is unable to interact with WindowServer.
Affects:
Potentially any MacBook with automatic graphics switching and NVIDIA graphics. Testing on Mid-2012 rMBP with GeForce 650M.
Potential Workarounds:
Downgrade to Mountain Lion. Mavericks 10.9.0 and up to 10.9.2 are affected to date. Your hardware is fine and you can reset the SMC and PRAM a million times if you want and not fix anything. If you want to use this as an excuse to have your Mac replaced, knock yourself out, they won't know the difference.
Use gfxcardstatus to force Intel graphics on notebooks. You will loose the ability to use external displays if Intel graphics is forced as the NVIDIA GPU is powered on indefinately whenever an external display is present.
MacBook Airs or any other portable Mac with Intel-only graphics are not affected as the crash is only suspectible while the NVIDIA GPU is active which these do not have.
Turn on the Remote Login feature in Sharing. Test using SSH to remotely login to your machine in the event of a hang. Issue a shutdown -r now to gracefully restart OS X (while improperly shutting down everything else open).
AppleCare response:
Useless. Did you reinstall Mavericks yet?