Yammer applies not one but three effects on all new messages in a feed: fade in, slide down and highlight.
However, this dynamic nature means that when you click on a button, the page doesn’t refresh but something does happen. The majority of websites still don’t use AJAX extensively, so some users may not be sure whether anything has happened at all or whether the button was properly clicked. To fix this, you need to provide some visual feedback for each of the user’s interactions.
Smashing eBook #17│User Experience, Practical Techniques, Volume 1│ 82