Jim has blogged about the DLR as Mary Jo Foley guessed.
Now we get a glimpse of what the DLR is:
It adds to the platform a set of services designed explicitly for the needs of dynamic languages. These include a shared dynamic type system, standard hosting model and support to make it easy to generate fast dynamic code. With these additional features it becomes dramatically easier to build high-quality dynamic language implementations on .NET. More importantly, these features enable all of the dynamic languages which use the DLR to freely share code with other dynamic languages as well as with the existing powerful static languages on the platform such as VB.NET and C#.
Good stuff. I am hoping this isn’t the last announcement and that we get to see the the Rails on the DLR demo? :)