Trend: Information Bars

Ever since IE first popped up the message “‘Did you notice the Information Bar?” websites have started showing notifications in a sliding bar at the top of the window. For example, Twitter displays a confirmation message in a sliding overlay when you save a change to your account. Is this any better than just showing the same message inline?

The Stack Overflow family of websites takes information bars to a whole new level, showing tips, status messages, and updates not just when the page is loaded, but asynchronously as you read.

What do you think makes an information bar effective without being intrusive? (Hint: asking “Hey, did you notice that?” should probably not be necessary!)