I mean seriously, if you work in IT, 5 days a week, at least 7.5 hours a day, you probably wouldn't want to look at code for the other 10 hours you're awake. If you have the time, and you're not doing household chores (cooking/cleaning) or looking after kids, you'd probably prefer to play games or do something else. Programmers do have other geek-ish hobbies you know. :) Those who consider IT people who don't program in their spare time as not being serious about their career are not very flexible minded. It's all about life style balance. Of course, programming as a hobby does add credit when finding a job, but being realistic, there's a lot more to life than just programming. There's like some stereotype thing that programmers spend all their time behind computers. Realistically, that's probably only if they're young or single... Other than that, I think the only time a programmer would feel the urge to program outside of work is if their work isn't satisfying enough.

a simple way would be to store resuable functions in files under one (library) directory.
For example, store I/O (input/output) operations in a file called library/io.php, math operations in library/math.php then require('library/io.php'); to reuse the functions.