I think it’s a continuum. Sure, I freely admit that I’m still rather ignorant when it comes to the low-level details of my computer. But compared to the understanding I get from Windows or Ubuntu? From that point of view, I’ve learnt a lot.

Besides, it’s not like this knowledge is useless. I now find myself being able to diagnose and fix problems with my system which previously I was clueless about. And it makes it a lot easier for me to learn the lower-level details if I so choose.

IMHO in most cases the "sense of understanding" comes from all the related materials which you read when installing a "difficult" system: it is difficult not because inherent complexity but for lacking abstracting tools (like GUI wizards) which forces the user to learn more in order to understand the "limited" provided interface. I remember my first (Softlanding?) Linux installs (by mid nineties) reading about hard disk geometry, the mandatory kernel recompilation for the network card drivers, the soft links when upgrading shared libraries, the monitor frequencies for X11, and a big etc. which previously (with DOS/Win 3.x) never had to deal with.