A while ago, a half-full tube of toothpaste was confiscated from me at the airport by some burly TSA jarheads. The tube held 6.4 ounces of toothpaste when full, so I guess it may have been above the 3 ounce limit when slightly less than half full.
So I figured I'd keep a tube of toothpaste that was well within the limit for use the next time I flew. When a tube got down to about 10% full, I set it aside rather than finishing it. But it was confiscated too! The guy pointed to the "6.4 ounces" on it and said it was too much. I noted that it was almost empty and so was in fact far below the 3 ounce limit. Then he seemed to get mad, and said that it doesn't matter how much is actually in there because they just go by what's printed on the label.