"From what's mentioned in the article, it sounds like some of the tasks that Beanstalk is being used for at PostRank are the same type of tasks that other companies, such as FlightCaster, are doing with Hadoop/Cascading."

Hmm, not at all. A message queue and a job queue are not necessarily one and the same. What we need is real-time scheduling, with up to the second resolution for each job. We don't run a batch "go fetch all of these pages" jobs, rather our system is always running, always fetching content. For that, a heap/work queue is required.