So I've been looking around and I can't find a Tilebrush or similar feature in Silverlight 4. Chatter on the internet seems to indicate that there is nothing built in. I am hoping that someone is going to show me the hidden camera, or let me know that it is some kind of sick joke. Is there really no Tilebrush or similar feature?!
It's not a sick joke. There really isn't a tilebrush. From what I've heard it's not yet in the new WinRT either.
Apparently it's a bit difficult to do with the way the silverlight internals are setup.
There are third party controls that let you do a tiled background. Here's one of them: http://nokola.com/blog/post/2009/12/22/Fast-Tile-Brush-in-Silverlight-And-Easiest-Way-to-Shader-Effects.aspx