I had the same issue. I was planning to have CSS 3.0 support in VS2010.
I installed Service Pack 1 because Microsoft says "We encourage all ASP.NET developers to start taking advantage of what HTML5 and CSS3 has to offer already today.", but couldn't see the support for CSS 3.0.
There is an extension from Microsoft, that installs CSS 3.0 Support only if you have SP1 installed and CSS 3.0 support is not there.
Click here to download and install the extension.