I have faced this issue when I decided to move one of my freelance project from my own TFS to CodePlex.
To re-assign to a new Source Control, you need to remove association to old one first.

Another case when you may need this is when you renamed your TFS and your projects cannot find their code storage and you will see this warning each time you try to open these projects:

Here is how to remove this association:
1. Remove all *.vssscc and *.vspscc files from your Solution folders.
2. Check if your Solution *.sln file is Read-Only. Remove this flag if needed.
3. Open *.sln file in an editor. I prefer Windows Notepad for such operations.
4. Find GlobalSection(TeamFoundationVersionControl) looking as showing below and remove it begining with GlobalSection and ending with EndGlobalSection:

GlobalSection(TeamFoundationVersionControl) = preSolution
    SccNumberOfProjects = 2
    SccEnterpriseProvider = {4CA58AB2-18FA-4F8D-95D4-32DDF27D184C}
    SccTeamFoundationServer = http://<YourTFS>/tfs/defaultcollection
    SccLocalPath0 = .
    SccProjectUniqueName1 = <Your Project path and name in TFS>.csproj
    SccProjectName1 = <Project Name>
    SccLocalPath1 = <Project Path>
EndGlobalSection

5. Save and close your Solution file.
6. Go ahead and open this Solution in Visual Studio IDE as usual.
7. If you will get IDE warning similar as shown below, just select "Permanently remove source control association bindings".

That's it! Now you can associate your code with a new TFS Project.
P.S. I tested this on VS/TFS 2010. Not sure if this works with older versions.

If you are on Windows 7, you probably have noticed about new feature – Windows 7 Jump List. If you right-click on an App icon (let say – Internet Explorer) you will see additional menu items which you as a programmer can handle in your solutions. If you are on Visual Studio 2008, the only way is to use an additional Windows API Code Pack for Microsoft .NET Framework. But there is a modern way for Visual Studio 2010 (at least for WPF):

• Open App.xaml file of your App
• Add reference to JumpList as shown below:

<Application x:Class="WpfApplication1.App"

             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"

             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"

             StartupUri="MainWindow.xaml">

    <Application.Resources>    

    </Application.Resources>

    <!-- Add reference to JumpList here: -->

    <JumpList.JumpList>

        <JumpList ShowFrequentCategory="True" ShowRecentCategory="True">

            <JumpTask Title="Notepad"

                      Description="Open Notepad"

                      ApplicationPath="notepad.exe"

                      IconResourcePath="notepad.exe"/>

        </JumpList>

    </JumpList.JumpList>

</Application>

If you need to create a GUID in VS2008 but this menu is disabled then you are facing the same problem as I did. Probably some options were disabled during installation. Fortunately it is easy to fix.

Copy two files guidgen.exe and Uuidgen.Exe form
C:\Program Files\Microsoft SDKs\Windows\v6.0A\bin
to
C:\Program Files\Microsoft Visual Studio 9.0\Common7\Tools
and you don’t even need to restart your Visual Studio.

Download Community Technology Preview (CTP) of Microsoft Visual Studio 2010 and .NET Framework.

I have met this problem when I worked on some Visual Studio add-ins:
VS Add-in Wizard does all work around to insert your add-in to Visual Studio menu "Tools" but if you want to make your add-in available in other menus, let say in context menu of Solution Explorer, you have to know some additional information about the place.
To get this know you need to add Registry value DWORD EnableVSIPLogging to  HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\9.0\General and set it to "1". Then just press Ctrl+Shift and do an operation you interesting in. You will get a dialog box, similar to this:

Don't forget to switch it to "0" (zero) when you will no longer need it because Visual Studio has many commands that start from Ctrl+Shift.
It works in Visual Studio 2005 SP1 or higher.