This is great! I especially like the live preview option!
Robert, when you have a stylesheet open, go to the Styles menu at the top and then you can use a designer to make or edit style rules! This is useful for those of us who aren't completely familiar with all the CSS options that are available! VS2010 doesn't have CSS3 in those designers but Expression Web 4 does have some CSS3 options in theirs which is fun to check out... especially the border radius options since it shows a preview of what it will look like as you change the parameters!