Silverlight PathTextBlock is a control that overcomes some of the limitations in the built in Silverlight 2 TextBlock, such as not being able to outline the text, and not being able to distort the text, for example to draw it along a circle.
Previously, you could use a tool like Expression Design to create the text and export it as a Path, but this wouldn't work for text that needed to be specified at run time. This control allows you to specify the Text property and it will generate the proper Path objects based on the font, font size, and text.
It is not meant to be a plug-in replacement for TextBlock, since TextBlock is a pretty sophisticated control. This is for the cases where you need one or both of these extra capabilities. A common use for this would be to jazz up your text in a game.