Ref12

http://visualstudiogallery.msdn.microsoft.com/f89b27c5-7d7b-4059-adde-7ccc709fa86e

Forwards F12 to ReferenceSource.Microsoft.com instead of showing metadata.

Microsoft recently launched a browsable version of the .Net reference source code at http://referencesource-beta.microsoft.com.

This extension lets you press F12 to open the source code for anything in the .Net framework.

You can easily jump to the actual source for things linq LINQ or WinForms or ASP.Net and see how they're implemented, including original comments.  Just place the cursor on any class, function, or constant in the .Net framework and press F12 to open your default browser.
No more "From Metadata" tabs! 

For source code or bug reports, see GitHub.com/SLaks/Ref12.

This extension currently only supports C#.  (the native C# & VB language services have nothing in common)
If you want VB support, let me know. 

When installing on VS2010, you will also need to install .Net 4.5, if you don't have it already.