I’ve used parts of Shell MegaPack by SSWare in a couple of small projects I did(Windows Forms), and was wonderfully surprised to find their controls fully featured, easy to use and customize and powerful in terms of abilities.
Their Windows Explorer GUI replacement Controls are the best I’ve seen on the market and can definitely help in making the Windows File system a part of your applications.
Apart from some minor annoyances (like this one which I had to find the hard way) and problems with earlier builds of VS 2005 (like this one), these controls work almost flawlessly, and are a mature product(version 7.1 already) to be used in real world applications.
Overall mark: 9.0. Great Product.
As an aside, I’ve also gotten a chance to use their excellent EZShellExtensions.Net product line, which helps in hooking those special file system events, and these guys know what they are doing.