One negative side effect to consider, it can be frustrating to the user to see a message then have it disappear and move on them. Especially an error message. Might want to remove the fade out and offer an [x] close button for errors.
A better approach is to add the notes to a placeholder that will stay on the page like gmail alerts. However, I have encountered long scrolling pages where the user needs ajax feedback and this notificaiton system was ideal.
*jQuery required. View HTML source for all neccesary code.