Once is generally enough. I did it awhile back and have tried to reference LFS for major changes that have been adopted since I last did it like EFI and LUKS. I'm glad to see it getting updates.
I ran Gentoo in college for a couple of years. Oh god the compilation.
I ran Gentoo for about a week a long time ago. On a 400 MHz Powermac G4. By which I mean, I installed Gentoo once and then decided I didn't like it.
It still works for PowerPC Macs :)
As someone who tried running Gentoo in the past, I could never find a decent resource for helping me figure out what make flags I wanted to set. It was far more confusing than FreeBSD, which at least provided rudimentary descriptions for each flag before compiling. I may have been missing something obvious though.
gentoo is too addictive, unless you want `emerge` as part of your routine