Global pen pals can promote deeper writing http://blogs.kqed.org/mindshift/2012/11/5-ways-to-inspire-students-through-global-collaboration/
I would say that some pretty specific guidelines need to be in place for writing expectations or you will get the informal writing style often received from beginners in blogs, wikis, etc. Things missing from this article: provide an exemplar writing example for students to use. This will set the bar for higher expectations from the beginning. Even graduate students use a different register for communicating with their peers than when writing for their professors. Don’t judge or make fun of their information style, just show them what you expect in the formal style and you may be surprised at what you get!