Visual Studio doesn’t have IntelliSense support for URL Rewrite by default. This isn’t a show stopper since it doesn’t result in stop errors. However, it’s nice to have full IntelliSense support and to get rid of the warnings for URL Rewrite rules.
RuslanY has released a Visual Studio schema update for URL Rewrite 2.0 which is available as a free quick download. The installation instructions (they are quick and easy) can be found here, which also include the schema for URL Rewrite 1.1.
The install takes effect immediately without restarting Visual Studio.
A side question commonly comes up. Can you get URL Rewrite support for Visual Studio Web Server (aka Cassini). The answer is no. To get URL Rewrite support in your development environment, use IIS7. You can set your Visual Studio projects to use IIS7 though, so you can have full debug, F5 or Ctrl-F5 support for IIS.