We had an interesting case here in New Zealand (reported on the News just before Christmas). A young girl working for a large retail shop was upset over having to work late in the build up to Christmas and said so on her blog. This was seen by the manager at the store she worked at and was then called in and her employment terminated. She was unhappy about this as 'she hadn't mentioned where she worked'. However she mentioned the store by name in other posts on her blog - saying how much she enjoyed working there.
This is something that people don't seem to understand - their blog can be read by anyone and come back to haunt them at a later time. As teachers we need to make sure that our students do understand about how emails and blogs are sent and how they are not secure and that deleting an email does not mean it has gone for good! Some of them are incredibly naive.