Rails 1.1.5 has been released today, but there are no new features. It's important, however, as it contains a number of bug fixes and a 'mandatory security patch' which David Heinemeier Hansson, creator of Rails, claims is significant:
This is a MANDATORY upgrade for anyone not running on a very recent edge (which isn’t affected by this). If you have a public Rails site, you MUST upgrade to Rails 1.1.5. The security issue is severe and you do not want to be caught unpatched.
Even though details of the security flaws are not officially being given, it wouldn't take a would-be hacker long to run a diff between 1.1.4 and 1.1.5, so if you're running Rails 0.13 through 1.1.4, upgrade as soon as possible. For more information see David's post at the official Rails blog.