Ignoring the argument which has sorta settled down here, I think there are three good ideas to do with this feature.
1.a. Explain on the dialog box which pops up when you lock messenger how to UNLOCK IT.
1.b. If 1.a. is not applicable then have the tooltip balloon pop up from the systemtray icon explaining you how to unlock it.
2. When you select lock messenger from the Plus! menu (an option I never even realised was there - I use shortcuts too much
) you get a dialog warning also - as how it is with using the key shortcut - MEANING that no matter how you do it, when you lock messenger for the FIRST TIME ONLY, you'll get the dialog box. Makes sense to me. Except you might need to change the words on the dialog box to get rid of "the key combination you have pressed" seeing as you haven't pressed a key combo you've selected a menu item anyway that's not important right now.
Offtopic: @Cookie yeah the interesting thing with Plus! 3 is that when it's installed alongside Plus! 4 when you go to lock messenger it doesn't change the icon, or stop sounds from playing when you receive a message. Which I think might have something to do with the fact it's default key combination for locking messenger is Ctrl+Space, which is now being used as a universal shortcut by Plus! 4, and this reason has been further proven to me when I've tried to make Ctrl+Space work with MP!3 and MP!L at the same time. Anyway so yeah I'm not a pro on the whole bosslock/messenger lock thing and how they may be different, but from my experiences using MP!3 and MP!L together since MP!L came out that's what I've seen.