With respect to this issue, it's my strongly held belief that one of the great features of the internet is that it lets anybody participate in the public discourse without having to be concerned with how it impacts your life otherwise. In addition, the potentially VERY PUBLIC nature of the internet makes the choice to hide one's identity the smart thing to do for most people. Not everyone has career in which current or future employment wouldn't be affected by what they post on a blog. Not everyone lives in an area with tolerant neighbors.
Any reporter who passes along without verification something they found on some random website somewhere is an idiot, but that has little to do with whether the identity of the person running the website is known or not.
...just adding, there's a difference between simply quoting an anonymous blog, as in "Internet commentator AlGoreRox asserts 'Bush is a big weenie'" and passing on unverified or unverifiable information from a blog, such as "AlGoreRox say Bush is a child molester." The latter is what reporters shouldn't do, but of course it's something they should be hesitant to do whether that's an anonymous blogger, a named blogger, or Karl Rove.