Late last week effectiveUI rolled out the User Interface Resource Center as a place for developers and designers to get information about various RIA technologies. They interviewed people from Adobe, Microsoft, and independent developers on a variety of topics. There's obviously a heavy user interface focus and they dive into specific examples like the eBay Desktop and general user interface guidelines.
The site should prove to be a good resource for people comparing RIA technologies. There are no direct comparisons (yet) but the articles they've compiled from Adobe and Microsoft provide a lot of information. I'm hoping to see them branch out into more technologies and more companies. They've also compiled an FAQ for the Three UI technologies on the site (Adobe AIR, Adobe Flex, and Silverlight).
In general this is a pretty good start for an RIA portal. With so much interest and confusion still around the RIA landscape, this should provide people with some good, unbiased information.