When to use Static Classes

I recently read this post about static classes and when to use them.  I found it a very useful and persuasive read.  Also it is good to know "why" to use object oriented code and not just blindly default to that design pattern.

It is for C#, but is applies to any language IMO.  Here static classes/methods can also be meant to be "functional" programming.

This was educational to me, so I'm sharing the wealth.

PS: I am still going to use static classes like String.trim() where there is no member data (stateless), and the functionality is VERY well defined and not likely to change.