I retired early because I realized that I would need about 20 years of full-time work to complete The Art of Computer Programming (TAOCP), which I have always viewed as the most important project of my life.
Being a retired professor is a lot like being an ordinary professor, except that you don't have to write research proposals, administer grants, or sit in committee meetings. Also, you don't get paid.
My full-time writing schedule means that I have to be pretty much a hermit. The only way to gain enough efficiency to complete The Art of Computer Programming is to operate in batch mode, concentrating intensively and uninterruptedly on one subject at a time, rather than swapping a number of topics in and out of my head. I'm unable to schedule appointments with visitors, travel to conferences or accept speaking engagements, or undertake any new responsibilities of any kind. I'm glad that the WWW makes it possible for me to respond to questions that I don't have to see or hear.
I miss teaching and daily interaction with students, but I get stimulating feedback by giving regular public lectures and speaking to informal Stanford seminars.
I'm proud of the 28 students for whom I was a dissertation advisor (see vita); and I know that 28 is a perfect number. So I won't be advising any more students. But I do say that if somebody solves one of the open problems stated in one of my Computer Musings, within about two or three weeks of the time I stated it, I'll sign their thesis. (After two or three weeks, I'll be working on something else and won't have time to read their work.)
I tend to spend about two hours per day in the library, about a half hour in DeGuerre Pool, and the rest of the time at home reading and writing, sometimes also sleeping and eating. I like to play piano and organ in the music room of my house, although lately I haven't had nearly as much time for music as I would like. If you're good at sightreading four-hands piano music, I have hundreds of pieces I'd like to try playing with you; please drop me a note and we can hopefully get together for a jam session. By the way, I'm also a big fan of the Stanford Theatre.
Of course I like to read nontechnical books, although I read very slowly. Here are some that I recently read and heartily recommend: