Dear Professor Mankiw,
I am a second-year assistant professor at the United States Naval Academy (I finished my Phd at UC Davis, summer '05), and regular reader of your blog and thought I might offer a slightly different perspective on your post: "Advice for Junior Faculty"--since many of your blog readers may be new faculty such as myself: at a school that places a lot of emphasis on teaching, but we still still need to publish in peer-reviewed journals to get promoted.
I decided to set up a blog this semester for my senior level class on monetary policy in order to foster class participation (and get the students to read the news, hopefully). I post a couple times a week (in the style of your blog and marginalrevolution.com) and then ask/require the students to respond to the posts. Their comments go towards participation points in the overall grade.
In this setting the benefits of a blog may outweigh the costs:
*A class blog is a way of connecting with students and providing a different way for them to participate in the course. This hopefully makes the course a more enjoyable experience for both teacher and student.
*A blog is a way to provide "innovative" technology into the course content; being online is a regular part of today's college student's lifestyle--this exploits that. Frankly, at a teaching school such as USNA (or comparable places, say, liberal arts colleges with around 5000 students or less), using a "fresh" teaching approach will be valued more, ceteris paribus, during tenure review than for those at a research school.
Finally, the costs are small if:
i) You post only a couple of times a week and keep the posts short (I also generally go with short articles on cnn.com).
ii) Your classes are small. I have approximately a total of 50 students across three classes this semester.
Lastly let me note blogs such as yours and marginalrevolution.com provide positive externalities for those of us at teaching schools. I can check them and then alert my students to the "day's headlines." If you're interested, here is the link.
Thanks for your time,