Namespaces - How deep is too deep

Any namespace that follows the logic of your application structure is fine - regardless of the length.

We have a namespace seven layers deep, with an eighth symbol on the end for the class. The dropdown in the top-left of Visual Studio 2010 that allows you to choose the class within this file doesn't fit our fully qualified class name, and when you mouse over it, there's no tooltip, so the only way to find the class name is to undock the source view and stretch it across two monitors.

I know this is dependent on the total length of the names, and not necessarily the number of nested namespaces, but I'm going to go ahead and define this as "too deep" :)

It can be handy to make your folder structure match your namespace structure, but it makes no sense to make a namespace structure match a folder structure.

The types and members of the namespace(s) are the things you are making. That is the output of your craft and the thing you should be concerned about. The files in the folder are a way to help you do so. You may have already structured the folders such that they match a sensible namespace (essentially you "wrote" the namespace structure when you did so), in which case all and good, but you may also have not done so. The namespaces will matter both to the creators of the assembly(s) and the users of it, the folder structure only to the creators.

Ignore depth, ignore folders, look at the spaces created by the names.