Hi I havve tried out wikispaces with my students and I think it works better for longer texts. Blogging is fine for starters and people who like to write regularly if you ask me. Check it out at http://norwenglish.wikispaces.com
Even though the chances of somebody going into your blog are quite slim, there is always the possibility that someone out there will read what you have written. It is much more fun that just writing to the teacher.