You can get an overview of what's in the box for developers by taking a look at the developer reference poster.
It's interesting to note that the supported languages are C#, VB, JScript, IronPython, VB10 (soon), IronRuby (soon). It's funny to see that they use "soon" for VB 10 (VBx), while VB 9.0 is still not ready...
LINQ is supported by Silverlight, but support for LINQ to XML is coming soon. Microsoft's XML Team has a word about this in this blog post.
Cross-posted from http://linqinaction.net