Some of the thoughts behind 3.x can be gleaned from Hugo Wetterberg's presentation from Drupal Camp Stockholm 2009. The link is dead.
In short the big changes from 2.x are:
- The transition to resources (with CRUD support) from rpc-style services
- Services endpoints can be placed on arbitrary paths in the menu system and configured completely independently
- endpoints can be disabled
- Endpoints can have debugging enabled
- Endpoints are exportable and can be packaged as features (with or without the Features module).
All this means that modules now can use services to expose APIs - a combination of services, a server and, optionally, an authentication method. And it's those who want to develop these API-providing modules, the services, servers and authentication modules, that is the intended audience for this preview release.
One thing we are looking into is Tests! We currently have tests for all administration tasks. The client->server tests have been written but do not have 100% coverage yet.
Documentation in progress
The links below are designed to help contributors get involved in Services 3.x. If you find any missing or incorrect information below, please feel free to correct it! Things will be moving along pretty quickly and parts of the documentation are sure to fall out of date.