Rails has been bundled with the developer tools for MacOSX since 10.5 - I admit that it was a bit annoying if you were compiling Ruby yourself in days prior.
Right - my issue was with the MySQL gem. The entire system is great because you can type
"gem install mysql" or whatever and it just works.
But the issue comes in when it doesn't work, which it didn't for me. It took hours of debugging. MAMP gets me up and running in < 5 minutes. A proper LAMP setup takes me < 10 minutes. I'm failing to see the advantage of Rails (at least from a setup standpoint) when it works perfectly most of the time, but fails so hard.