I have been watching the Gearman project for almost two years now, played around with it a little but never considered putting it in production because of the lack of persistent queues. With the release of version 0.6 I am going to have to take a serious look at it.
As you may know, PushButton Labs, my new company, just acquired GreatGamesExperiment.com (aka GGE). GGE does a ton of background tasks, reading and building hundreds of rss feeds, computing game recommendations, popularity, etc, etc. A perfect job for Gearman. We have our own job queue system right now that gets polled from cron once a minute, but there are a few jobs that need to be done NOW. Gearman could help solve this problem and make it much easier to scale the site later.
I will let you know how it goes. You can check out the Gearman Project Page here.