Login shell vs non-login shell

A very good note with regard to login shell and non-login shell - http://unix.stackexchange.com/questions/38175/difference-between-login-shell-and-non-login-shell. It basically covers every aspect that needs to be known, along with relevant configuration files under each circumstance, and notably the behaviour of the Terminal app in OS X in the comments area.

Update 2023: Another relevant blog post emphasizes the sequences that startup files are triggered in each manner. It also offers intuitive scenarios when different manners should execute.