New York Times has migrated their popular WPF-based New York Times Reader to the Mac, using Silverlight and native Cocoa windowing and application logic, and using the Safari / WebKit API as a Silverlight wrapper. (Darn it, I knew it was both doable and legal!)
It doesn't have the text flow feature that WPF was so fantastically good at, but being as text flow is rumored as "coming soon", either for NY Times' reader or for Silverlight, I'm pretty excited about the future of that.
I blogged about the feasability of this (native, non-web cross-platform apps with Silverlight rendering) just days ago, motivating myself to outright buy a Mac since I didn't see anyone bothering to try. Now that someone has not only tried but succeeded and released a significant product based on it, I feel a little mixed -- part bummed that I didn't get to post first-discoveries, but part excited that Silverlight has potential for an Adobe AIR-like wrapper, both technically and legally.
The NY Times Reader for Mac sure isn't running on WPF, though, and it shows. The user experience is clunky and the lack of text flow is painful (try resizing the window or scaling the text). The whole thing is nothing like the WPF version, except only for the initial screenshot appearance (without interacting) and, perhaps, the actual content.