[tnecniv]

This is probably one of those things that varies a lot based on what your field is and how close to academia you stay while in industry. It's going to be a lot harder to come back to doing experimental physics if you spent 5 years as a software engineer.

[eastWestMath]

Right but someone who has a realistic chance at being hired as a professor won't be working as a commodity software engineer, they'll be in some sort of specialist/research role. Any of the job offers I've seriously considered leaving were to be a computer scientist.