A few projects are using parallel_test to speed up their tests/specs. One project has had the best results by running one less parallel spec than the number of cores on the machine, unless of course you only have one core.
Another team discovered an odd bug in RubyMine where they could not click-through “require spec” or run specs if their project had code in vendor/plugins that extended ActiveRecord::Base. Here is the RubyMine ticket they filed.
Finally, it looks like a Linux machine running Ruby 1.8.6 patch 287 had rounding errors when using the ActiveSupport helpers for 2.days.ago. They fixed the issue by upgrading to Ruby 1.8.7