Proposed addition: Note that it is not possible to log in to both LiveJournal Messenger and MSN Messenger, Windows Live Messenger, or Windows Messenger at the same time. Logging in to one will automatically log you out of the other.
I'm not sure where to put this addition. I was thinking we would stick this right under the paragraph that goes: "When LiveJournal Messenger is active, it will appear in the lower right corner of your browser window whenever you are viewing any LiveJournal page, except secure (https://) pages such as the checkout section of the LiveJournal Store. You will need to log in to LiveJournal Messenger with your Windows Live ID to launch the service. Once you are logged in, the LiveJournal Messenger window will display a status area and your contact list."