Tooltips is always a good usability practice to display descripitve and meaningful message on UI, which provide guidance and extra information to users visually. However, I cannot find this kind of handy "control" in the latest version (40412) of the AJAX control toolkit. (Feature request?)
The traditional HTML "title" or "tooltips" tag of control cannot make the users (nor even developers) happy, so I searched and found this Tooltip Extender control today. It is nice and handy for...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.