- campaigns & marketing
- creating new business entities; with offline support
- adding new relationships to entitites (not just new attributes)
- client-side validators and scripting support
- customizing activities
- workflow for activities and custom entities
- better CRM e-mail integration with Outlook 'inbox' and 'sent items'
- separate tables for custom entity attributes/relations
The use of a separate custom attribute/relation table for each entity extends the number of fields you can add to an entity in version 3.0, thus improving on the current limitation which is kind of an "official secret". MSCRM 1.2 is limited by the SQL Server 8K row-size restriction because all fields are added to the entity table (actually less because of replication overhead). This is especially hurtful for the contact entity as it is 80% full out-of-the-box in version 1.2.
To make a long story short, Mattew Wittemann has published a nice summary of the white papers, with several sceenshots, which is available here. Recommended reading!
The Microsoft MSCRM 3.0 white papers can be downloaded here (feature overview) and here (discloses new customization options).