Hi,
Currently there is no moderation built into the blog comment system. If you really need to implement it right away you could clone the blog and then build on what is there for the comment system. Currently you can get notification of comments and you can delete them.
I do realize the current bog comment system is rather weak in features, but rather than fix it, what I plan (as indicated on my road map) is to build a more general comment system that can be used across features, not just in the blog, but to make it easy to implement comments inside any feature like for example to allow comments on a product in the webstore feature. I don't want to build it over and over in each feature so I'm going to build it into the core, then I will replace the current comment system used in the blog with the new one. I also plan a provider model so different comment systems can be plugged in like to make it possible to use external comment systems like Disqus or Intense Debate or others.
Hope it helps,
Joe