What is the “Nudge” feature? How do I use it?
The “Nudge a friend” feature allows you to send an email to a user on your Friends list who also lists you as a Friend and hasn’t updated their journal in the past week.
To use it, click the small button with a picture of a hand in the blue toolbar at the top of any other user’s User Info page. You will then be taken to a page where you can either confirm that you wish to send them a Nudge or receive an error message stating that you cannot Nudge this user. Alternatively, you can view a list of your Mutual Friends who haven’t updated recently and choose to Nudge them from there.
What is LiveJournal’s Friends system? How do I use it?
I don't like the wording of that last sentence but can't think of anything better at the moment.