Maybe this is a temporary issue. I will check later in the night today and update/close this thread. [2013-02-27] For most of the world, this issue should now be resolved and non-repro, and the general consensus is that it was a Google glitch!
I searched for 'StackOverflow' on Google UK, both via the Omnibar and the Google UK homepage. The resultant URL: www.google.co.uk/#q=stackoverflow&...
Displayed results (larger image):
Actual page on doioig.gov (larger image):
This has no resemblance to the content displayed by Google.
I have tested this using Chrome Incognito without logging into Google so there is no search bubbling and also no plugins on Chrome that are playing these tricks.
I am not tagging this as a bug as it seems unlikely that this is an issue within Stack Exchange control.
stackoverflow on the US or some other region specific site, this effect is not observed. But searching explicitly for
stackoverflow doioig brings up a slightly different result: