In other words, if a file has been opened for editing, the shell explorer/file manager would mark it. I see this being useful in networked environments, where opening a file usually prevents other users from interacting with it. This could also be implemented as a special "Open Files" folder, containing shortcuts/aliases to the files in question.

Buy a Mac. You can highlight and append notes to each and every file on the disk. Then you can use the built in "Spotlight" app to locate what you want with a click of the mouse. This is a good idea and you can hope that poor Windose users will see this feature in Vista.

I suppose the obvious solution is to open a special directory devoted to files under development and then transfering the files to the appropriate directory when they are complete.

You might also change the file properties (read only, hidden, archive) to provide similar functionality.

I like the idea of color coding the file names based upon a configurable development status. Just a popup with a user definable list of label names and font colors that could be accessed by right-click on the file name would be nice. Make it an open architecture so that programs like Word, Excel, ... can use the feature transparently.

In the new Windows Vista, there is a feature called "push pin", which allows you to identify files you commonly work with, and place them in easy view.