Designing a fade-out or and auto-close of a message -- a form of "anticipating" behaviour -- is a greater challenge for your design and designers.

I would

 1. start with just making it easy to dismiss, and not auto-close it
 2. try get a feel for if it is needed make it auto-close, by letting users use it over time,
 3. then, if needed,  make it fade away

It all depends on the situation, and on how your users will end up using your system. You would **decrease the risk of failure** -- for example users finding it hard that things are "blinking" too fast or not grasping exactly what happened -- by choosing not to auto-close it.


Related question: [Is it bad design to hide a form's success message after a short time?][1]


  [1]: http://ux.stackexchange.com/questions/18161/is-it-bad-design-to-hide-a-forms-success-message-after-a-short-time