I've just been reading about blog directories and how they affect search engines. If we are maintaining a blog, should we be thinking about submitting the blog to some of these blog directories?

There's an article about this on SEJ, it also lists some good blog directoriess:
http://www.searchenginejournal.com/2...-blog-to/5998/

Not saying that you would spend a lot of time doing this, but maybe try a couple of the "good" ones?