At UCT we required a Gradebook REST webservice to retrieve all grades for all students in a site.
We implemented this locally based on earlier work by Aaron Zeckoski for the iClicker integration. The UCT GB EB can be found here (r8087):
This feature request is to consolidate this extra functionality into the existing GB entitybroker REST endpoint. A current limitation however is that the iClicker work and hence derived UCT GB code is GPL-licensed so cannot be included in trunk Sakai unless its first relicensed.
In future we may also have a requirement to get all grades for a student for all sites in which they are a member (which could also be used for a 'my grades' widget for example).