I have been playing a bit with Tarpipe. This service allows users to pipe together services from third parties. So send an email, have the attached image uploaded to Flickr and post the resulting picture URL to Twitter.
The idea is great, but it is not yet robust enough. I was only able to get an workflow run twice. And some other activities are in the pipeline (I hope). The Dropipe application ended with an error message. It can be that the service is now overloaded due to its exposure on ReadWrite web. So I will come back to it later.
The documentation still needs a lot of work. It is totally unclear what some services do.