Leopard will have Ruby 1.8.6, Rails 1.2.x, Mongel, Capistrano and
Subversion pre-installed as “first-class” citizens into the OS core.
Meaning they don’t live in /usr/local nor /opt directories. I believe
they are installed in /bin. So you shouldn’t have to worry about it
overwriting your installation. Just make sure your install directory
shows up before /bin in the system $PATH environment variable.
That being said, given that Leopard will include nearly the latest
releases of Ruby (and not a broken one) and Rails with most of the
standard goodies, why not just use them. If they are not completely up
to date just use RubyGems to update them. This is what I’ll do once
Leopard is released. Heck as much attention as Apple is putting into
Rails these days, we just might see them upgrade as Rails does with
the standard software update mechanism (one could dream anyway).