I haven’t see that. At best, you can use the extensive support of CSS styling we got with 1.3 to mimic native look and feel, but that’s a big job! Not even sure how to deal with various themes we got on modern systems…
I suppose the point of RIAs is to bring their own look or to be flexible enough to allow to do your own shinny look, not to look like a random bland application on your platform… 🙂
(Now, if I like skinnable applications, I also appreciate GUI frameworks using native controls or looking as such, like Qt (vs. GTK+ for example), precisely to provide good old “bland” applications not breaking user experience.)