Depends on the purpose of the blog. I maintain a blog for two reasons. One, writing about problems and their solutions as if I'm explaining them to someone else is a great way to solidify the concepts in one's mind (similar to rubber-duck debugging[1]). Two, having an active blog is a signal to potential employers that you're active in the ecosystem. Even if someone is rehashing the same old topics in their posts, seeing how they think and how well they write can be a useful indicator.

[1]http://en.wikipedia.org/wiki/Rubber_duck_debugging