It’s been said that meta keywords and description tags are dead. Where as I’d agree with the keywords tag, the descriptions tag I’m no longer convinced is dead. Actually, it’s quite important; especially for blogs.
If you use the site: command in Google, and look at Google’s descriptions (aka snippits) for a blog, you may notice some indexing issues. Usually one of two things happens. Either your blog description is generic and includes things like the date and categories, or your blog’s description is exactly the same. The second one will probably land a lot of your pages in the supplemental index.
If you check out Matt Cutt’s blog, you’ll notice that the descriptions start with the date followed by time, categories and then the first few words of his post.