The .NET beta has been available for a few weeks now. I've been spending a little time with it everyday and I have been finding many wonderful things. For instance, the Base Class Libraries (BCL) have been extended - with several new namespaces and lots of new classes.
A couple of my favorites.
Compression Libraries
Support for GZip. See the new System.IO.Compression namespace.
Access Control Lists (ACL)
At last, Microsoft has added support for manipulating ACLs.
Learn More
There is a complete list of new BCL features at the BCL blog. Check it out.