I think it might be interesting to note that different people have different motivations for "side projects" (as well as different definitions for side projects!).

For someone, a side project might be about solving arbitrary problems such as trying to write a Tetris clone under, say 1024 bytes on x86-64 Linux machine -- something which has absolutely no real world relevance whatsoever, while for someone else that'd make no sense and be waste of time. Probably they'd much rather build something much more concrete, say a real product (say a web app) actual people can, and hopefully will use.

Perhaps it is a meaningless and arbitrary attempt at making distinctions, but I find it relevant for myself as I certainly fall under the first example, while many here in HN fall under the second. I feel this definitely plays a role in what we consider "side projects" and how we deal with them.