CloudAMQP is now an AppHarbor add-on
We've just added the CloudAMQP queue service to the AppHarbor add-on catalog. CloudAMQP is based on RabbitMQ, a mature message queueing system with good .NET client support. The CloudAMPQ guys have written a great guide on how to use the service from AppHarbor hosted applications.
Using queue services like CloudAMQP is a good way to coordinate tasks between AppHarbor web- and background-workers. Instead of completing time-consuming jobs (such as sending emails) synchronously while processing a request, you can enqueue the job, return a request response to your user and have a background worker pick up the message and asynchronously complete the job. Using this pattern will help you build more responsive and robust applications on AppHarbor. We expect to soon have a tutorial and screencast on the topic ready.
We're excited to expand the AppHarbor offering with a solid queue service and we look forward to your feedback on the CloudAMQP add-on!