To be sure, there are some great things about this job. To first approximation you are your own boss, and even when it comes to teaching you typically have a tremendous amount of freedom. It has often been said that being a prof is like running your own startup -- you have to hire the staff (the students), raise the money (grant proposals), and of course come up with the big ideas and execute on them. But you also have to do a lot of marketing (writing papers and giving talks), and sit on a gazillion stupid committees that eat up your time. This post is mostly for grad students who think they want to be profs one day. A few surprises and lessons from my time in the job...
Show me the money. The biggest surprise is how much time I have to spend getting funding for my research. Although it varies a lot, I guess that I spent about 40% of my time chasing after funding, either directly (writing grant proposals) or indirectly (visiting companies, giving talks, building relationships). It is a huge investment of time that does not always contribute directly to your research agenda -- just something you have to do to keep the wheels turning. To do systems research you need a lot of funding -- at my peak I've had 8 Ph.D. students, 2 postdocs, and a small army of undergrads all working in my group. Here at Harvard, I don't have any colleagues working directly in my area, so I haven't been able to spread the fundraising load around very much. (Though huge props to Rob and Gu for getting us that $10M for RoboBees!) These days, funding rates are abysmal: less than 10% for some NSF programs, and the decision on a proposal is often arbitrary. And personally, I stink at writing proposals. I've had around 25 NSF proposals declined and only about 6 funded. My batting average for papers is much, much better. So, I can't let any potential source of funding slip past me.
Must... work... harder. Another lesson is that a prof's job is never done. It's hard to ever call it a day and enjoy your "free time," since you can always be working on another paper, another proposal, sitting on another program committee, whatever. For years I would leave the office in the evening and sit down at my laptop to keep working as soon as I got home. I've heard a lot of advice on setting limits, but the biggest predictor of success as a junior faculty member is how much of your life you are willing to sacrifice. I have never worked harder than I have in the last 7 years. The sad thing is that so much of the work is for naught -- I can't count how many hours I've sunk into meetings with companies that led nowhere, or writing proposals that never got funded. The idea that you get tenure and sit back and relax is not quite accurate -- most of the tenured faculty I know here work even harder than I do, and they spend more of their time on stuff that has little to do with research.
Your time is not your own. Most of my days are spent in an endless string of meetings. I find almost no time to do any hacking anymore, which is sad considering this is why I became a computer scientist. When I do have some free time in my office it is often spent catching up on email, paper reviews, random paperwork that piles up when you're not looking. I have to delegate all the fun and interesting problems to my students. They don't know how good they have it!
Students are the coin of the realm. David Patterson once said this and I now know it to be true. The main reason to be an academic is not to crank out papers or to raise a ton of money but to train the next generation. I love working with students and this is absolutely the best part of my job. Getting in front of a classroom of 80 students and explaining how virtual memory works never ceases to be thrilling. I have tried to mentor my grad students, though in reality I have learned more from them than they will ever learn from me. My favorite thing is getting undergrads involved in research, which is how I got started on this path as a sophomore at Cornell, when Dan Huttenlocher took a chance on this long-haired crazy kid who skipped his class a lot. So I try to give back.
Of course, my approach to being a prof is probably not typical. I know faculty who spend a lot more time in the lab and a lot less time doing management than I do. So there are lots of ways to approach the job -- but it certainly was not what I expected when I came out of grad school.
Update 4/24/10: Thanks to Mike Belfrage for pointing me to this interview with Niklaus Wirth where he echoes some of the above sentiments.