I was browsing around the exchange and noticed a speck of crud on my screen. Only, when I tried to wipe it off, it turned out to be part of the site. Have a look at some SE question between the "link" and "improve this question" links.
On Mac Safari 5.1.2 and Chrome 16.0.912.75 I see a speck:
It goes away when the mouse is over "improve this question", but comes back on mouseout. (For Safari you have to mouseout on the "link" side to get it back.)
Now I can't not see it.
Please make it go away
I don't see this on FF 8+, but that's cold comfort if I'm not using it at the moment.