I find the analogy also holds like this:

Unlike the do-it-yourself hot rods of the fifties, one of the implications of calling a car a "ricer" is that it's composed of a bunch of bolt-on performance enhancing kits and accessories. You get the feel that you've built a hot rod, and all the tweaking and fiddling needed to keep the bits from falling off or out of sync makes you feel like quite the mechanic, but you're not an engineer or a machinist.

In like manner, all those meaningless messages scrolling off your screen too fast to read when you do an emerge world make you feel like some 'leet coder, even if you wouldn't know what they meant if you _could_ read them. Yeah, you can get under the hood and mess with the USE flags and the package masks - but you're really just pressing the same button as someone using aptitude.

Yeah, you learn a lot about how to fix the gentoo package sysetem, but it's gentoo specific knowledge, seldom applicable to any other linux distro.

Source packages, and instructions on how to tune and rebuild them, are available for all of the binary distros I know of.