I've finally gotten around to starting coding up a little GUI for my little petshop sample. It follows the 
MVVM pattern. After doing just a couple of windows it's clear that any GUI implemented using MVVM will have a lot of view models and a lot of commands. So where should I put all those classes in terms of folders? I see two possibilities: 
- Put all the view models in one folder, and all the commands in another folder. There might be more structure below these folders.
 - Put each view in a separate folder and put the view models and commands belonging to the view in the same folder.
 
As to what works out best...I'm on the fence...