Mercury Messenger Service 1.8 - Popular Pick

Mercury Messenger Service can do the same things as your normal messenger:

Talk to friends
Change your nickname and status
Add a display picture (also known as an avatar)

But Mercury Messenger Service has some extra functions that your normal messenger doesn't have, for example:

Be online with several MSN adresses at the same time.
Login with your status on 'Invisible' or any other status you want.
Have a different MSN name in every conversation
Use and create your own plugins
Default plugin added: a FileServer for MSN using IRC like commands

See when someone starts a conversation with you (before he says something)
See when someone closes the chat conversation window.
See who added you into a conversation with multiple people
See when someone deletes you from their contactlist.
See the difference between MSN and Mercury Messenger Service users
See your fake and fakes friends (Explained in FAQ)
MSG+ colors
and more...