[mortenjorck]

The problem with half of these is the unnecessary use of spatial metaphors.

Flipping, scrolling, or otherwise moving the un-highlighted text to make room for the highlighted text doesn't accomplish anything – it's the same text, just with a different presentation.

Save these spatial animations for progressive disclosure. When you want more information to pop out of something, or you want additional controls to present themselves when the user has entered a specific context, that's when you should consider scrolling and flipping your elements.

[edoloughlin]

Agreed. The animations where the background or the lines around the text transitioned were nice, but the first few times the text flipped or was replaced made me move my mouse away to check that I wasn't missing something. Some of the effects (e.g., bolding) clipped the last letter from some of the words (Ubuntu 13.04, FF23 with a minimum font size set).