I did not have this problem with previous versions of Safari.
Might be an extension or third party plugin installed that was compatible with the prior version of Safari but not 6.
Check Safari > Preferences > Extensions
If there are any installed, turn that OFF, quit and relaunch Safari to test.
If it's not an extensions issue, go to Safari > Preferences > Security
Deselect: Enable plug ins
Quit and relaunch Safari to test.
If that helped, follow the instructions for troubleshooting here.
I am having the same issue on reddit.com After returning from a link like imgur.com, the original page will show for a bit and then disappear to this white screen. It seems like the browser is continuing to load the page after the blue bar has finished its journey across the address field. The page technically has loaded the links as I can click on them, but cannot see them. If I press the escape key, the page will finish loading correctly. It doesn't always happen tho. I have all browser plugins disabled. Using Safari 6.0.2 on 10.8.2 It is more of an annoyance than anything...