Last year, I became the first person to publish in a peer-reviewed academic journal under a blogging pseudonym. Earlier this year I did it again. I can now announce that I'm also (I think) the first blogger to act as a peer reviewer under my pseudonym. The manuscript was submitted to a well-known journal and 'Neuroskeptic' was asked to evaluate it. The request came to my neuroskeptic email address, and I submitted it as "Dr N Skeptic" - my real contact details etc. never being involved. Which is... nice. But I don't want to say much more about it, because of confidentiality. So I'll take the opportunity to say that in general, peer reviewing a manuscript is not very different to writing a blogpost about a paper. There's a lot of overlap in the thought-processes involved, and the skills required. However, while I love blogging, I've never enjoyed being a peer reviewer. As a reviewer, you're not just commenting on a manuscript, but also sitting in judgement on it (the final decision is the editor's, but they mostly go along with the reviewers.)
I don't like wielding the power of being a reviewer. I worry that having said power makes me responsible for any flaws in the paper if it does get published, or alternatively, that I'll be responsible for hurting the authors' feelings (and careers) if it doesn't. But the worst part is that I will never really know what part my review played in the story of the manuscript. You never know whether you were right or wrong. What I like about blogging is that it's all above board. If I make a mistake then readers can correct me. If I write something profound then people can let me know. Eventually, in the process of open dialogue, the truth will out. It'll all come out in the wash. As a peer reviewer, you rarely get that sense of closure. It's an important role to play, and all scientists have a duty to take part in it. But that doesn't mean we have to enjoy it.