The Alice Project http://aliceproject.wordpress.com/ is a great example of using collaborative blogs in an English classroom.
“Would you tell me, please, which way I ought to go from here?” - asked Alice -
“That depends a good deal on where you want to get to,”- said the Cat -
“I don’t much care where –”- said Alice -
“Then it doesn’t matter which way you go,”- said the Cat -
“–so long as I get somewhere,”- Alice added as an explanation -