In Cocoa apps such as TextEdit and Mail, if you select a full line of text by triple-clicking, you can then deselect words by command-double-clicking on them. If you copy the resulting selection, the deselected words are replaced by line breaks.
I realised this when I tried to open a URL in TextEdit by simply double clicking it. When that didn't work, I tried double clicking it with different modifiers. I still think it's stupid that Cocoa doesn't offer the functionality that was available via Internet Config in System 7.
Mac OS X Hints
http://hints.macworld.com/article.php?story=2006010301395537