To Charge or Not to Charge Shop Batteries?

With all the battery powered tools nowadays, I have a question on storage of them. Should the battery be stored charged or flat?

Simon Watts: Batteries should be stored charged. They get into bad habits if allowed too long a rest and may become lazy and decline to accept a full charge.

Michael Dresdner: For practical purposes, I leave mine charged. That way they are ready to use when I need them.