I suddenly noticed that today the upvote icon and the flag icon disappeared from all comments on stackoverflow.
I looked at the HTML, they seemed to be there, but my IE7 (running on XP SP3) won't display them.
I do see the number of upvotes for a comment though.
I did all sorts of
Ctrl+F5'ing and it didn't help.
I also have a stupid feeling it happened after I went from stackoverflow to meta where I wasn't logged in (and probably don't have enough rep to vote up comments) which magically affected my ability to see/use these icons on stackoverflow, too. But it's probably not the case. Just a stupid feeling.