Rails controllers, safe to fork a block and then return?

Question

Short and simple question:

fork { something_that_takes_a_few_seconds_and_doesnt_concern_the_user }

respond_to ...

Is there any reason not to do this sort of thing in a rails app? In PHP we're currently relying on external queueing systems like beanstalk or Amazon's SQS coupled with an asynchronous task worker that's pulling things off the queue to run in the background. A simple fork would fit better in many cases, depending on the complexity of the task.