On the Social TNT blog, Chrisopher Lynn makes the great point that corporate blogging is not like other marketing channels: it's about fostering a dialogue rather than broadcasting a message. He uses the great analogy of locking yourself in a room and just talking away.
He goes further and says it's not enough to just lurk and write up a synopsis of what you read - you need to actively get involved. Treat it like a conversation and remember to say something back that is meaningful (not just repeat back what somebody says to you).
On the whole I agree with Christopher's position, although I do see one exception: the corporate news blog. This can work particularly well for agencies and companies that need to be perceived as thought leaders in a particular field. SearchEngineLand jumps to mind as one example of what is sometimes called a signpost blog - that is a blog that exists solely as a reference point to the latest happenings in a particular field.
However, if you are new to blogging, I would encourage you to read Christopher's post - thinking of blogging as conversing is a great way to build reputation for your blog.
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