Since it bit me this morning, I'll tell you, hopefully, before it gets you too. Ruby on Rails 0.13.1 and Ruby 1.8.3 "don't quite get along together":http://groups.google.com/group/comp.lang.ruby/browse_thread/thread/640eb8b71c302cc2/9a9fe872ba2c5989%239a9fe872ba2c5989?sa=X&oi=groupsr&start=0&num=2 just yet. So, stick with Ruby 1.8.2 for the time being.
Debian users who run the latest Unstable packages will need to manually hold ruby1.8 until it's safe again.
