With Silverlight 5 the Bindings in Styles feature was added, which is pretty useful.
Silverlight 4 doesn't support that feature, but is there any way to simulate this using Silverlight 4?
There is a potential work around here.
http://blogs.msdn.com/b/delay/archive/2009/11/02/as-the-platform-evolves-so-do-the-workarounds-better-settervaluebindinghelper-makes-silverlight-setters-better-er.aspx