Weblogs/ Wikis

I have worked with some colleagues who use wikis to share their class assignments and materials.  Both of these colleagues were computer teachers so they were housed in a computer lab for their classes.  I on the other hand have never work with blogs or wikis myself so have not even thought of implementing them into my classroom.  The more I use this blog and get more comfortable with it, then I might be able to transfer that to my students.  I believe the main concern is that once something is posted it is there forever and like Richardson mentioned all it takes is one parent to read an inappropriate post and it would be over.  I understand that expectations should be taught first to try and prevent this, but reality is that some students will post inappropriate writing or pictures anyways.  Then what would be the consequence?? Not using the internet, which would force the student to not have equal access to the material.......Thinking about all of this makes it hard to wrap my head around all that can go wrong compared to the benefits of collaborating and tracking learning.  Since I teach high school math, I am trying to brainstorm how I can use a blog for my students.  Since math is concrete and many problems only have one answer, I don't think it would be too helpful to post problems because once one student answers the problem is solved.  I am thinking maybe there are open ended type problems that can be solved multiples ways and the students can discuss options for solving and what is easiest for themselves.  I think it would be difficult to assess because not all my students have internet at home and we do not have computers in class or the time to take each week to go to the computer lab to blog and stay on course with curriculum requirements.
As far as wikipedia is concerned, we try to tell our students not to use it as a source because anyone can edit it.  After reading the section, I never had realized that their were so many corrections and edits made in such a short period of time based on accurate information.  I don't know that that will change the school's view that it should not be a resource.  I personally think that I would rather start with a blog forum that can be monitored by myself for editing and blocking of posts before I would want my students adding to wikis online.