Currently Visual Studio will turn strings that look like URLs into hyperlinks (eg http://www.codeplex.com/hyperAddin), however it would be even more useful if these hyperlinks to refer to other parts of the code base (using symbolic lookup) or can be easily defined by the user. This allows you to create quick links to related code, or create an overview description that can then be linked to from many places in the code base.
There is a prototype of this defined as a Visual Studio Addin at http://www.codeplex.com/hyperAddin. This should be integrated into Visual Studio itself (and improved, like having spell checking, warnings on broken links, and intellisense when creating links).
Please see the help for the hyperaddin for a complete feature overview.
In addition to the hyperlinking feature, the addin also does word-wrapping in the comments. It can fix up formatting when words are added or deleted (currently you have to invoke a 'Format' command to fix up a comment, but you could imagine doing it as you type). This is a trivial feature, but a real time saver (because adding just a few words to the middle of a paragraph wrecks the word wrapping).
Both of these features encorage commenting in a code base, which in general is a very good thing. Please consider adding this in the next version.