You are going to love this:

http://www.leapsecond.com/great2005/

The short version is that this guy hauled three cesium atomic clocks up a mountain while on vacation with his kids. They returned 23 ns older then the guy's wife (who stayed home to study for her nursing board exams).

Note that time dilation isn't just caused by motion (special relativity), but also by proximity to a gravity well (general relativity).

Time dilation of everyday life is so small that it's not detectable to all but atomic clocks, over the course of your entire life. So the differences between 10 miles is so negligible it doesn't even exist as an issue.

It doesn't practically exist as a problem for things (like people) for whom a meaningful time scale is around a second, and a lifetime 100yrs.

If you are operating on very small time scales, or if you're going to be around a long time, it can matter a lot.

Good luck with your GPS navigation then. "You are here. (Give or take 10 miles, no biggie, eh?)" There is a surprising number of applications in your everyday life for which Newtonian physics are not precise enough.

Why would it be relevant, then, for a programmer to know that?

A programmer working on something like the OPERA neutrino experiment would need to account for those factors [1].

GPS devices also have to account for relativity [2], so programmers working on those also have to factor that into the logic.

[1] http://www.telegraph.co.uk/news/science/science-news/8905322...

[2] http://physics.stackexchange.com/questions/1061/why-does-gps...

Mostly it's not. Charitably, someone writing software for e.g. a particle physics experiment might actually need to account for altitude to produce accurate results.

Of course, that's the sort of domain-specific demand that might not belong in a general-use list. People writing sound engineering software have to worry about all kinds of subtleties with sample rates and harmonics, but I wouldn't put that in a guide to basic data I/O - I might not even put it in a basic analog-to-digital guide.

Who knows, the next great interview question could be asking it.

The writer may have been exaggerating their point.

Also, you have to account for the different gravitational field in both situations, which affects time flow.

Yep. And it's measurable, it's just very, very small. It normally doesn't really matter for all but the most sensitive applications.