Capture Exceptions with Instrumental (tested in Rails 3.2.11)

exception_reporter_middleware.rb

# lib/instrumental/exception_reporter_middleware.rb
module Instrumental
  class ExceptionReporterMiddleware

    def initialize(app)
      @app = app
    end

    def call(env)
      @app.call(env)
    rescue Exception => e
      I.increment("app.exception.#{e.class.name}")
      Rails.logger.debug "Notifying Instrumental of #{e.class.name} exception..."
      raise
    end

  end
end

instrumental.rb

# config/initializers/instrumental.rb
require 'instrumental/exception_reporter_middleware'
I = Instrumental::Agent.new("MY_API_TOKEN")
Rails.application.config.middleware.use Instrumental::ExceptionReporterMiddleware