RVM, which is a standard tool to manage Ruby versions, does expose trunk:

  mil:~ poet$ rvm list known_strings | grep ^ruby
  ruby-head
  ruby-1.9.3-rc1
  ruby-1.9.3-preview1
  ruby-1.9.3-head
  ruby-1.9.2-p290
  ruby-1.9.2-p180
  ruby-1.9.2-head
  ruby-1.9.1-p431
  ruby-1.9.1-p378
  ruby-1.9.1-head
  ruby-1.8.7-p352
  ruby-1.8.7-head
  ruby-1.8.6-p420
  ruby-1.8.6-head

However, in my anecdotal experience most people run patch releases.