I think Terence Tao is one of the few professors in mathematics for whom the professorship market is truly liquid, and his salary history reflects that. His salary has skyrocketed to over $430k:

http://ucpay.globl.org/index.php?campus=&name=Terence+Tao&ti...

All the faculty getting paid more than him tend to be physicians and surgeons.

For comparison, the average pay of a tenured professor at Harvard (highest paying university on average) is "only" $198k: http://www.thecrimson.com/article/2013/4/10/harvard_salaries... Tao isn't even at Harvard and he's paid over double the average for tenured faculty there. I can only assume UCLA is forced to match what he could get if he left to a place like Harvard.

Terrence Tao is a far stronger "get" than the average Harvard professor.

He is brilliant mathematician, eloquent educator (from introductory to proffesional topics), and a thought leader (with Gowers) in the mathematical research community on meta topics like research style.

Of course, that's the point. It takes such talent in academics to command the sort of job liquidity at the high end that is taken for granted in industry.

That Terence Tao is being paid twice the average tenured salary at Harvard while he's at UCLA speaks to both our points. Unlike most professors, Terence Tao is paid by UCLA what he could hypothetically get if he went to Harvard (speculatively, of course). Other professors would face much more friction in packing up their bags and hopping into tenured positions at peer institutions or higher.

It's quite common to move between tenured jobs. Typically you don't have to go through the whole six-year pre-tenure odyssey again. Applying for a tenured job is still quite a process, but that's often true for positions outside academia too, especially senior professional positions.

"Quite common" is an overstatement. The market is nowhere near as liquid. Only a small number of tenured jobs are advertised each year compared to the number of junior tenure-track jobs. Superstars can get hired somewhere else, but for the vast majority of tenured faculty there are not many options (most universities would prefer to hire a cheaper junior faculty member, and many are very limited in how much credit they can give an applicant towards tenure).

Whether it's "quite common" may vary a lot from department to department; in some places my statement may perhaps have been too strong. In the places I've seen firsthand it's quite common for tenured faculty to sometimes interview elsewhere. I did so, and made a jump.

This is also a common strategy for people angling for promotion or a big pay increase -- get an offer elsewhere, and then use that offer to get a promotion at your current institution. I'm not recommending it, but I've certainly seen it done. Common outside academia too, of course.

I can't speak for experiences outside my field, but generally movement happens in the senior academic market by word of mouth alone.

I have never heard of a tenured professor taking a position at another school without retaining tenure.

Well, that makes sense, no sane professor would give up tenure, so any new university job they take would obviously have to offer tenure from the start.

afterburner meant professors are very unlikely to give up a tenured professor position for an untenured professor position. This is quite different from giving up a tenure professor position for a non-academic job.

My point is never say never. A sane person might give up a tenured position for a variety of reasons.

If you're saying that people leave tenured positions for non-professor positions, sure, happens all the time. But if you have tenure already, any professor position you get at another school will also be tenured. It would be an insult if a school offered a non-tenured position to an already tenured faculty.