I had originally come to the Feathermoon forums to try to round up those who are still active in the IC Twitter Project, but a quick search of your forums makes it look like it never reached here? Allow me to explain it then! :)
ICly your character finds a "magic book". They're stacked all over the place in cities, you could find it on a dead body, someone could cheat you and sell you one (they're usually free), your character gets his or her hands on one any way you want.
Your alt might jot down a note into the book and get surprised when people respond to it, or maybe they were told how it works, or maybe they just see conversation going on between other users and have an 'Ah ha!' moment.
Their name goes on the cover (it becomes your "book name", which can be your character's real name or some nickname or description or anything really), and you ICly write names of others into the back (the people you OOCly follow). If you decide you don't like someone writing in your book, you just strike their name from the back cover (OOCly unfollow them).
Never used Twitter before? No problem! Many of us in the project (me included!) learned it for IC use. It's surprisingly fast to learn and easy to use. Once you have an account, you go to an active person's feed (*cough* Mine, for example. I'm Sunthistle on Twitter: https://twitter.com/Sunthistle ) and follow some of the active names. The more people you follow, the better! Interactions are what makes this fun. :)
Any messages sent "in the front of the book" (regular Twitter messages, public messages) can ICly be seen by anyone. Messages sent in the "back pages" are private, only to one person (OOCly PMs).
A lot of people wonder how one RPs over Twitter -- the messages are so short! They are, but that makes it more fun (sort of like writing drabbles). RP is anything from lighthearted stuff to heavier topics. And remember, if you don't like the tone of someone's Twitter RP, you can ICly or OOCly strike them from your book. (The book can add or delete names on its own, to cover this kind of thing.)
RPing over Twitter is not only fun, it's really handy. You can sneak some RP in at work, RP between classes, while waiting for an appointment, whatever. Since the book is IC, you can read it or close it as it fits into your OOC life. Plus Twitter RP often leads to RP in-game, which is an added bonus.
The thread for the original project on WRA is here: http://us.battle.net/wow/en/forum/topic/1083748924 , if you'd like to look it over.
I've been RPing over Twitter for nearly a year now, and have written almost 15,000 IC tweets (and I'm not even one of the old timers!). This is a big, long term IC thing. (Alas, as WoW is slowing down, so is the project. I'm hoping when MoP drops, it'll get really busy once more.)
It doesn't matter what server you're on, all are welcome! Currently WRA and MG are the two most represented servers in the project, though we have some TB folks too. It would be great to add some Feathermoon folks to the mix! :)
Feel free to post questions if you have any. I look forward to RPing with you all over Twitter!