It's always easier to target an audience that you are familiar with and are a part of. Since I would have bought this book myself if someone else had wrote it I knew what people would want to know and how to reach them.

If I were targeting the book at sysadmins, for instance, I would have had no idea how to get in front of them or talk to them at their level.

re: pricing, nope. I think the discounting works because it's intermittent and gets people sharing. If I were to lower the price permanently I wouldn't expect sales to remain that high.