I was so intimidated by the whole "build your own system" philosophy, that I never tried, and it was only after asking on HN for advice[0] that I finally gave it a shot.
Software-wise the best decision of my life so far.
It also taught me that "RTFM" is often the best solution, and that man pages are there for a reason.
If I break something, I can fix it. Guaranteed. That's not completely due to the experience you gather doing the "manual installation of everything" dance, but also due to how this process works. I've never had to reinstall my Arch system - there's always a way to save a botched installation.
As someone who likes to tinker with my systems sometimes (and who's reinstalled more screwed up Ubuntu/Fedora setups than I can count), that is really valuable to me.
Around 2 years ago, I wanted to tinker and understand linux distros and have installed most of them. But, when I tried Arch, I settled with it,no more tinkering. However,I find it painful to install. I installed Arch successfully in third time.