Since my last
update some changes have appeared in the steps needed to create a patch using Wix. The good news is that you no longer need MSIMSP to create a patch (and all the hurdles required to obtain MSIMSP).
Pyro is the new tool that can be used instead of MSIMSP and streamlines the patch creation process.
For more information about Pyro and how to use it you can use
this link
Also
here you can find "updated instructions for building patches using the new WiX v3.0 patch building system".
With this information Wix gains new strength, and
it seems that Wix will be incorporated into Visual Studio Rosario (the one after Visual Studio Team System 2008, just released), instead of existing infrastructure for creating Windows Installer packages.