Resque Bus uses resque-retry and resque-scheduler to do exponential backoff. That is, it will retry immediately, 2 seconds later, 4 seconds later, and so on up to several hours.
It was a little tricky to make sure it ended back in the right application queue, but it worked. If it was put in another one, it would crash because the code to process it would not line up.
That is interesting, I was looking for something similar to an EBS for PHP time ago, but eventually I wrote myself an ad hoc solution which uses MySQL (and row locks) plus a gearman worker and cron.