Mongoid requires fixed versions, this is pretty annoying, for example, when I want to run the CarrierWave specs, I get stuff like:

/Library/Ruby/Site/1.8/rubygems.rb:280:in `activate': can't activate activesupport (= 2.3.4, runtime) for ["mongoid-0.9.9"], already activated activesupport-2.3.5 for ["activerecord-2.3.5"]

All versions should be specified with '>= 2.3.4', etc...