Web API will gradually replace Organization service and Organization Data service to become single web service for Microsoft Dynamics CRM.
Authentication is provided by the application itself when used within web resources, form scripts and ribbon commands.
Maximum 5000 records can be return for each request.
Web API Authentication
HTML web resources
you don't need to write code for that.
In each of these cases user is already authenticated and authentication is managed by the application.
SSRS Reports in CRM 2011 Online
Dynamics CRM 2011 Online now supports custom SSRS reports. There's a bit of setup required, though, including the installation of BIDS (part of SQL 2008) and a (free) add-on for CRM known as the Report Authoring Extension. In this video I go through the setup and show some basic SSRS authoring techniques.