My only real experience is with MongoDB, which we chose for queuing because we were already thinking of using it for our main document store. It flopped, entirely. Queue systems are generally very high write...you're constantly grabbing values while at the same time modifying them.

I think if we had used any *SQL database we would have been fine. Although they don't necessarily have high write compared to a lot of in-memory/distributed systems, they certainly do better than a global write lock.

I haven't ever used Postgre so I don't know of its queuing capabilities. If it has things like atomic modify-and-read, then you'll be fine. After the MongoDB debacle, I went to another company and we used Beanstalkd for a dedicated queue...couldn't have been happier. The protocol is dead simple, and it's so beautifully geared towards being a queuing system that I'll probably never want to go back to any other DB for queuing =]. Worth a shot if you need a queue and have the resources to run it, otherwise I bet Postgres will work just fine.