Installing the most recent version of Ruby on Snow Leopard
You should use RVM, the Ruby Version Manager. It allows multiple side-by-side installations of Ruby without affecting the system Ruby installation, which as another commenter pointed out can potentially be problematic (or at the very least, tiresome to maintain).

It allows you to quickly and easily install the latest patchlevel of Ruby, past Ruby versions, or even alternate implementations like JRuby, MacRuby, or Rubinius.

To install:

$ bash &lt; &lt;(curl -s https://rvm.beginrescueend.com/install/rvm)


Once it's installed, setting 1.9.2 as the default is as simple as typing:

rvm default 1.9.2


And if you feel like switching back to 1.8.7 temporarily:

rvm use 1.8.7