There has been quite a few posts on Prism on many blogs and some comparing it against AIR and Silverlight. Thought will give it a shot to see what this new hype is about and to me it looks more to like an application that allows you to create a shortcut to a webpage on your desktop (the only difference being that you need not open a new window for yourself but Prism does it for you when you click on the link :) ). It looks to me like an XUL application which provides you a way to run a webpage "like" a application on your desktop and I don't think it qualifies "yet" to be called as a Web Platform or even any closer to that.

I think there is nothing to seriously look into this at least at this moment or when probably it supports offline synchronization of some of the most popular apps.