At Pronovix we've been thinking about distributed service systems. I was asked to do some background/proof of concept research, and after one day, here is the first experimental module, called remote blocks. The first thing what I want to say about this module, is that the access control is currently omitted, because I haven't find a really easy and clean way to do it (something what works in 5 minutes). On the first screenshot, you can see the module's admin interface in my Drupal sandbox.
Currently there isn't so much setting here. But here you can enable the server mode, so that other sites where remoteblocks are enabled, can pull data from your site. It can be a better solution to refactor this functionality to a different module, but now it is OK.
This is where you can add block to your site. If your JavaScript is turned off, then you will have 3 textfields (URL, module, delta). If JavaScript is on, then it hides the module and delta textfield (as you can see on the screenshot), and based on the URL, it asks the remote block server of the available modules and deltas.
As you can see, it is really easy to set it up. It may makes sense to remove completely the module part, and put all available delta into one list, but this is rather an usability issue than a technical one.
After you have added the block, you can edit or delete it under the "List" tab. The delta is represented by a number, because currently I don't store the $block['info'] in the database.
This is where the remote block is enabled, and it fetches data from a different site (in this screenshot actually it fetches from the same site, because I was lazy to set up a new site). I hope that I can do some further experiments in this exciting new area. The module is published on Drupal.org: http://drupal.org/project/remoteblocks
