I have mixed feelings about side projects. Sure it sounds good and looks good but let me tell you my own example.
I am a single core processor.
I am pretty much capable of doing pretty much just one thing at a time. I've tried to multi-task to the point of switching off from what I'm doing at work to something else but it just doesn't work. One or both of them suffer.
I tend to be engrossed in what I'm doing at work. If I'm bored with what I'm doing I'm in the wrong job and that just doesn't last long before I throw in the towel.
Sometimes I'll work on that problem more. Sometimes I'll just do research/reading on that or related topics.
But I just don't really have the knack of switching off from solving that problem and picking up something else with equal vigour.
I have the same issue when it comes to learning new programming languages. I tend to have limited success when doing it on my own. Where I succeed is when I HAVE TO learn a new language, typically because that's now my job.
It reminds me of the scene from Swordfish where Travolta and Jackman are being chased in the car by a hit team, Travolta hands over the wheel to man the machine gun. Jackman says "I don't know how to drive this." "Learn!" was the response.
I get the feeling that the US (I'm Australian) has cultural differences that come into play here. For example, the education system in the US seems to have a very strong focus on extracurricular activities, something that doesn't seem to exist (to anywhere near that degree) in Australia. This includes sports, social clubs, community service and so on.
So much so that it can be an important part of getting into the right college and then the right graduate school (Australian universities, at least when I got my degree, typically just looked at your Tertiary Entrance Score and that's about it; in fact the whole system was AUTOMATED on that). The TES being a scaled combination of exam and coursework.
I wonder if there is a culture of multitasking because of this?
Whatever the case... I am a single core processor.