In my Visual Studio Tips and Treats talk, I discuss proper code commenting for ASP.NET pages. Let's review.

It is generally a bad idea to use regular HTML comments to comment out ASP.NET server and user controls. Why? Because the commented controls still be parsed and rendered. Imagine commenting out a large data grid, but still having all that content sent to the client. Worse yet is sensitive information that has been 'removed', but is still showing up in the client-side source.

Example:

<!--<asp:Label ID="Label1" runat="server" Text="SocialSecurityNumber" />-->

The recommended approach is to use server-side comments (Ctrl+K+C). Server-side comments prevent the commented code from being parsed and sent to the client.

Example:

<%--<asp:Label ID="Label1" runat="server" Text="SocialSecurityNumber" />--%>

Now for the good part. I just discovered, by accident, that you don't need to highlight the entire region you want commented. You can simple place the cursor inside the tag you want commented, and use the keyboard command Ctrl+K+C to comment, or Ctrl+K+U to uncomment. Up until now, I had either used the mouse or Shift+[Down|Up]Arrow to select the region I wanted to comment out.