Hot on the heels of the Silverlight 2.0 release last week is a beta version of the AOL RIA mail clientpreviewed at Mix08 and built on Silverlight 2.0.
(I just signed up but who knew their contextual advertising would catch on so fast!) Although the beta is missing the "HALO" theme featured at Mix08, it does feature 3 themes including Onyx (the default, shown above) "classic" which is themed similarly to a number of other AOL web properties, and a Hubble space theme.
Cursory analysis of the app suggests the vast majority of it is built in silverlight, including (it seems) the editing widget which at the time of Mix08 was still being done with DHTML. We'll do more digging and let you know.