What does Arch Linux have to do with developing Ruby?

Don't have to wait 6 months and upgrade everything to get slightly newer versions of packages. The packages are pretty direct from upstream instead of being patched and split apart by the distro.

What advantages does Arch Linux have over Ubuntu?

The main one: Packages don't end up 6 (or more) months out of date between updates.

The maybe a advantage (if you agree with the OP)/maybe a disadvantage(if you like me, don't): Much more manual configuration.

Been a while since I used Ubuntu, but you can typically install newer packages from pre-release versions. You're not locked in to the 6 month upgrade cycle.

I think it's a pretty good model. For 90% of the installed software there's really no reason to update packages more than every 6 months.

Read at Dho's link. My primary reason for the switch was that I wanted to learn more about Linux.