The terms 'login' and 'logout' are used in WordPress in an inconsistent way. The correct usage is this: 'login' is a noun, and 'log in' is an act (a verb). Menus that offer the action of logging in should say 'log in' and log 'login'; menus offering the action of logging out out should say 'log out'. Also, at least one place in the site admin area in the upper right says 'Sign out' instead of 'Log out'. And, finally, instead of saying 'Successfully logged you out.', just saying 'Logged out.' would be much better.
It'd be nice if WordPress were fixed so that 'Log in' and 'Log out' were used consistently and correctly when an action is being used, and 'login' and 'logout' were used when referring to the account (if necessary). I did this in my own blog by doing a case sensitive earch for 'Login' and 'Logout' and fixing this required hacking a few of the core files, so as soon as I upgrade to the next version, these changes will be lost. This is why it'd be nice to see this fixed in the mainline version.