A commenter asked how I choose my reviewers, a question I rarely get (except in the form of "Can I review for you?"). Most of my reviewers were inherited from the previous SF/F/H editor, who had several years to find really good writers and mostly weed out the really poor ones. I didn't really like the style of a few of his reviewers, so I showed them the door and went about replacing them with my friends.
Okay, that's not the entire truth, but it's certainly not false, either. I've been involved with the genre writing community since I was a wee young thing, and I've gotten to be friends with some excellent writers. LiveJournal, conventions, and KGB readings have also turned out to be great ways to connect with potential reviewers. When I needed reviewers, I turned to people who I knew were fast readers, articulate and thoughtful writers, used to the pressure of freelance work, and extremely familiar with certain areas of the genre where I felt we had some gaps in our reviewing lineup. I was specifically looking for people who knew a lot about horror, as we had been relying on one or two people to review all the horror books that came through here and I felt we needed some fresh perspectives.
While an all-around generalist is a wonderful thing when you're on a tight deadline, for most reviews I want someone with in-depth knowledge of a particular subgenre. I have two reviewers who mostly cover paranormal romance, for example. Others know doorstopper fantasy, or cyberpunk. We have one military SF specialist and at some point I'd like to find another; I spread some of it around to other reviewers but it would be great to have someone else who really knows it. When I was reviewing I specialized in anthologies and collections. Our needs change depending on what's popular, so the Lovecraftian horror reviewer isn't getting much right now while the ones who handle
The reviewer doesn't actually have to be a fan of the subgenre. One of my reviewers is a horror author who hardly ever reads horror. He'd rather read classic SF. I send him horror to review anyway; because of his work, he knows a great deal about who's doing what in the horror field right now, and I actually rather like that he's not a Rabid Fan, because it means I get more thoughtful, nuanced reviews. I try to remember to send him some of the stuff he actually likes from time to time to keep him happy.
Right now we're in a pretty serious book drought; I have no idea where all the big summer books are, but so far I've gotten only five titles for May, June, and July. That means I'm hard-pressed just to keep feeding my twenty or so regular reviewers. Once I start looking for new reviewers--assuming the drought lifts, which doesn't look likely for some months--I'll probably go through my archives of emails from people who want to be reviewers, looking to see what particular areas they're interested in and how that matches up with what we need. It's both wonderful and sad that there are far more terrific reviewers out there than we could possibly employ, but at least that means I get to be very picky about it.