Creating a Centralized NuGet Packages Folder

I would imagine most people by now will have discovered and use the NuGet Visual Studio extension (http://www.nuget.org/). It is a great way of adding and maintaining 3rd party code libraries in your projects. One problem I find though is that every time I create a new project or solution I end up installing the same old NuGet packages. By default NuGet downloads the source code for these packages into a new "packages" folder in your project/solution root directory. This means I have the same source code downloaded multiple times, in multiple locations. This can easily be fixed as you can...