Kevin Schofield from Microsoft has a post on their education blog entitled "Should Teachers Blog".
I've been thinking aobut this for a while. I've been trying to think of reasons why not to blog. And I can't think of any. Teachers should blog, just like they should talk, write, draw pictures etc. Anything which helps get the message accross.
Having said that though, although I blog, I don't blog about the courses that I teach as such. I tried it a couple of years ago, when I wanted to blog my C# course for the first year undergraduates. You can see how it went here. Not good. I found that a Wiki is a much more sensible form of narrative when working with directed courseware becuase it is not as linear. So I ended up with this instead. However, I don't expect much action on either from students, although it would be nice if there was.
A recent article in the Guardian in the UK pointed at statistics which said that if you take 100 people, out of that number 1 will be moved to blog regularly and around 10 will be inclined to comment on the blog. And the other 90 or so will just read it. Or not. We have around 140 or so in our first year cohort and I know that quite a few of them blog reguarly so in that respect we are bucking the trend. (we do get quite a lot on our forums though - which is encouraging)
I tell our students that as an exercise in improving the communication and writing skills, as well as giving them a wider audience for their work, a blog is a really good idea, and well worth exploring for that reason alone. It can also be fun.
Nowadays I use my blog to pull out particular themes that I think are important to students and also to "humanise" me a bit (scary thought), so that people are more inclined to come and chat because they feel that they know me more on the basis of my blog. I also blog because I enjoy it.