Hi,
I also have those "funny" screenshots in Safari, mostly when using a TYPO3 CMS backend. What I saw was some Microsoft things when screen started blinking. So first I thought maybe the combination of MS Office and Silverlight plugin in Safari could be the case. So Silverlight has been deactivated (remove silverlight.plugin from /Library/InternetPlugins).
The problem startet in the afternoon on Nov. 4th with a freeze, after the Update to Yosemite on Nov, 1st. The small popup with the "A graphic problem has been found" came again and again when I clicked on report or ignore. I then even could not connect my Thunderbolt Display - the display had no reaction.
One day later, in the evening, I had a freeze again, but after restart, the popup had gone. Strange.
AppleCare could not help me out so I had a meeting in the Apple Store on Monday. They did a Hardware Test via Network and everything was fine. So they took my Macbook Pro early 2013 and did a fresh Yosemite install.
As I need the Mac for my daily work, I could not test very long with the fresh install, just about 10 minutes, but there was no error. So I took the migration tool and copied back the backup from Time Maching (which took 6 hours for 520GB from an external TB harddisk). On Tuesday evening, the blinking and freezing in Safari came up again.
So on Wednesday i removed Silverlight, but the error came again, also today.
This time I was lucky to find this post, so I could tryout the helpful tip to deactivate the automatic graphics card switch. Since then (about 7 hours) the Mac runs without error.
But please, Apple, I´ve bought an over 3.600 Euro expensive machine to be sure to have one of the best tools for my daily work as software developer. I think the hardware is fine, but Yosemite has it´s problems. I hope you´ll fix that issues asap.