If the person who answered this question is right, you cannot put a binding as the value in a setter in a style in Silverlight. Which is a shame, because I have 4 textblocks
Here is how its done. You use a ContentControl and specify a ControlTemplate for it as a static resource:-
ContentControl
ControlTemplate
Now you can bung as may other properties with bindings in to the Control Template as you want.
This approach could be extended to Style:-
Style