One cool Vista feature that hasn't been talked about enough is the built-in .Net Framework 3.0.  What's even more cool is that it's also available for XP (through a separate download).   

To prove it, the team put together the New York Times Reader, a free download available at http://www.nytimes.com/timesreader.  It's a standalone app that pulls all the day's news from the New York Times and presents it in a nicely-readable way.  The news is stored offline, so after a short sync, you can take it with you on a plane or someplace without Internet access and reader the morning paper!

Our speech team is shipping the managed speech API in .Net Framework 3.0, and to demonstrate it we added a TTS feature to the reader.  Go to the top of the screen and click "More".  Then select "News in Pictures".  At the bottom of the screen there will be a button labeled "SPEAK THE NEWS".  It uses the new, human-sounding Microsoft Anna voice.  Unfortunately that feature is Vista-only.