According to rails.info Rails 3
requires either Ruby 1.8.7 < p248 or Ruby 1.9.2dev because everything
in between has bugs. That's quite unfortunate seeing that the MRI core
developers haven't released any fixes for the bugs yet, yet Linux
distributions are eager to package the latest version (p249).
We've backported the bug fixes that affect Rails 3 to p249 and
included these in the latest REE release, 2010.02. I think the
documentation should be updated with this fact.
Can someone with some clout (maybe DHH as he’s most recognisable) send emails to the owners of these other domains and ask them to serve a 301 header to the official docs. There are so many domains and Google indexes them all, it can be hard to know which one is the right one.