Side Projects and your Full-Time Job
Programmers who partake in side projects have a significant advantage career- wise over those who don't. There are millions of reasons that this is true, but one such reason is that of hiring.
Given two nearly identical candidates, with the exception of side projects (e.g. candidate A has none, while candidate B writes programming languages on the side), candidate B will almost certainly get an offer before candidate A.
Of course this assertion is due to the perception that if one is motivated enough to work outside of work, and eager enough to learn new technologies they'll have no trouble taking on more demanding tasks, or tasks which require a decent amount of "ramp-up."
However, there is another side of this coin. Programmers who actively work on side projects might be thinking more about their side projects than their actual job.
Perhaps to them, "work," is just 40 hours of "Hammock Time".