Wintellect published 69 page whitepaper about programmatic differences between Silverlight and WPF.

I scanned it quickly and I didn't quite read it in details, but it definitely looks like a material worth studying if you are developing WPF and/or Silverlight applications. As a special bonus, at the whitepaper's end, there is a topic about code reuse strategies which looks really interesting knowing that Silverlight is generally considered to be a subset of WPF and that Microsoft is committed to bringing Silverlight and WPF closer together with the each release.