This is extremely disapointting. I have an early 2011 MBP 15", and I experiece the same display artifact issue when the display goes to sleep. I use this MBP both with and without my thunderbolt display.
At one point it started to get so bad that I could not see anything and my laptop became completely useles.
Here are some of the things I tried to remedy my situation,
1) Did an 'Option' boot and started up from the 10.9 recovery partition. No artifacts (even though booting into the installed OS resulted in a completely unusable state, which required a hard reboot).
2) Used Disk utility while booted on the recovery partition to verify the disk...no repairs needed. Ran a repair anyway just to see if it helped...No help...
3) Booted in recovery, erased the partition, and did a clean install of Mavericks, then reloaded my files from Time Machine. After this attempt the MBP is usable when booting to the startup disk, but the artifacts are still there, especially when the display sleeps.
I am very unhappy with this, as it appears to be a software issue (since there is no issue when booting to the recovery partition), and it has impacted my use of this laptop for over a month now. To the point where it was unusable until I did a clean install and TM Backup recovery (which took almost 8 hours of my day).
This is a critical flaw, and unacceptable. These issues seem to be happening more frequently with Apple post 2011, and I worry it is cause for concern. I dont want to see more of the late 90s Apple, that launched failure after failure. I like the early 2003-2010 Apple which produced innovation after innovation, and proved to be the market leader.
FIX THIS!