First tried creating default Rails app using Rails 3-beta3
$ rails simple
$ mate Gemfile gem 'rails', '3.0.0.beta3'
$ cd simple simple kristianconsult$ rails s /Users/kristianconsult/.rvm/gems/ruby-1.9.2-preview1/gems/ activesupport-3.0.0.beta3/lib/active_support/values/time_zone.rb: 208:in `utc_offset': undefined method `current_period' for nil:NilClass (NoMethodError) from /Users/kristianconsult/.rvm/gems/ruby-1.9.2-preview1/gems/ activesupport-3.0.0.beta3/lib/active_support/values/time_zone.rb: 222:in `<=>'