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GitHub User: jnicklas
@7: CarrierWave has built in support for MiniMagick, which does the same thing Paperclip does: shelling out to ImageMagick directly. I'd really recommend taking another look at RMagick though, it's far more stable these days, I've never had a problem with it.
@14 Juan: IIRC validates_size_of works with CarrierWave at least on ActiveRecord and Mongoid.