Ever been browsing through a link-heavy paragraph of text in Safari, and had a tooltip appear when your cursor innocently hovered over a link? The problem is that if you then move your mouse, the tooltip will "follow" the cursor. Tooltips for other links will then appear instantly, rather than after a delay, as is usual.
One solution is to move your mouse out of the text area, but a quicker fix is to tap Enter on the numeric keypad, which you can do with your mouse-hand thumb. The tooltip will disappear and won't return until the mouse is moved to another link.
[robg adds: At first, I wasn't seeing the tooltips in Safari 2. Then I remembered I had put them on permanent vacation with this hint. Tooltips appear to be disabled by default in Safari 3, though the referenced hint (with 1 at the end instead of 0) will enable them.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20070726084307698