I'm lucky enough to be getting paid to write stuff against Whidbey right now. Although the tooling leaves something to be desired, the APIs are pretty solid, and it's been interesting using the new stuff. Today, I came across a namespace that I think falls squarely into the “I could never give up the CLR libraries, and now they're just getting better” camp:
It has classes like GZipStream in it. The wrap a regular stream, and compress or decompress whatever you pass through it. Nice, eh?