The reason why my Make text appear and disappear in Silverlight 2 didn't work anymore after some Silverlight updates is because I used the Mouse Down event on the button. After the update the correct way of making a button work is the Click event. The Mouse Down event works with shapes and other objects such as this rectangle:

Update 2009-01-07: After grahamws' comment I have added to the button and the rectangle animations a text affected by the Visibility property. In its normal state it's Collapsed and it is set at Visible in a 2 second timeline. This to show that now in Silverlight 2 Release the Visibility property works fine unlike at the time when I played with it in a previous Silverlight version.

You can see all the code in my comment from 2009/01/07.