Scott Guthrie, the "father of .Net", frequently talks about the features of Orcas on his blog. I was fortunate enough to catch one of his seminars when he was here in Phoenix. Very smart guy and not nearly the spin doctor a lot of Microsoft employees tend to be.
http://weblogs.asp.net/scottgu/Some elements of Orcas is are downloadable now (i.e. Linq, DLinq and XLinq and portions of C#3.0 have been available as "beta" to plug into .Net 2.0 for quite some time)
Linq is going to be huge: Object relational mapping done natively.. As well as Lisp-ish lambda emition of code... Ajax will officially be supported. There's rumor that Iron Python will find it's way into the .Net professional distro as well.
The learning curve for .Net (well, to utilize it's more advanced functions) is going to get substantially steep pretty soon.