1. There are too many of them
2. You have no idea if there is anything useful in them,
3. People who ought to be writing blogs, often don't get round to it. There are people who aren't blogging, who really should be.
4. The quality of material is wildly variable - much of it is opinion, little of it is knowledge. There are people blogging, who really shouldn't
I would summarise the situation as "too much noise, not enough signal".
Now if there really is knowledge that needs to be "pushed" within an organisation, then a blog could be a pretty good way to do it. If there is Signal, and you can separate it from Noise, then a blog is a good Carrier (to continue the metaphor).
For this to happen, then
1. The person who should be doing the pushing, needs to see it as an important part of their role. They need to blog, and should blog.
2. The people who need to receive the knowledge, need to know where the blog is, so they can "tune in" to it (i.e. follow it)
3. The number of blogs within the organisation is managed, or limited, to minimise noise. This means a policy of "blog if you ought to" rather than "blog if you want to".
Let me give you an example. Say there is an IT community in an organisation. Say there is a head of IT security, who regularly needs to send out updates, alrets and other material to that community. He or she could use a blog (with email notification to the community). That way everyone will be notified, and the updates can be found on the blog site, for future reference. Notifications come through email, but Outlook is not the main storage site. However for this to work, there needs to be
1. One IT security blog
2. One person who sees it as their job to blog the updates and alerts
3. A community of users, with a vested interest in reading the blog.
Now let me say right now that I am talking about blogging within an organisation, as a way of sharing knowledge for business purposes - for continuous process improvement, and for better decision making. This is a different context from blogging on the world wide web, where people blog for many other reasons, including for self-expression, for profile building, and for social networking.
Here's another example. Imagine a community of practice in an oil company, focusing on some technical topic (borehole stability, seismic processing, expandable tubing). The community has a forum where they can raise questions and give answers, but also a community blog, moderated by the community leader, where the core community members or other subject matter experts can share validated knowledge with the community. It's a way of pushing out new knowledge. But there needs to be only one blog, with a group of people who see it as their job to inform the community, and a community of interested readers. This is a different purpose and a different mechanism from the chatter that goes on in the community discussion forum.
So if we add some process and some accountabilities to the blog software, we can end up with a useful approach which should convince the cynic. But if there are no accountabilities and no process, then we can end up with the situation the cynics describe - too much noise, not enough signal.