Here is a summary of the changes to this version:

New and updated topics Description of changes
  Updated the file SDK Readme.htm with known issues and workarounds. This can be found in the download version of the SDK at msdn.microsoft.com/MBS/Downloads/CRMdownloads/default.aspx.
Accessing Web Services Added new topic that explains how to access the Microsoft CRM Web services from your custom scripts.
Callouts: Supported Callouts for Entities Bug fix: removed Route from the list of events for which callouts can be triggered.
Callouts: Support for Version 1.2 Post Callouts Added information on enabling version 1.2 post callouts after upgrade to version 3.0.
Client Programming Guide: Form Object Model Updated information and samples for:Form Properties  

Lookup Field Type

Customer Field Type

Date/Time Field Type
Client Programming Guide: IFrame Support Added information about passing parameters to an IFrame. Also added a note regarding support for IFrames in the Outlook Client.
CrmDateTime Bug fixes in the description of supported formats for date/time strings.
CrmService Entities Completed attribute documentation for all entities.
CrmService Enumerations Added state and status reason mapping to all state enumerations.Added values to all enumerations.
CrmService Messages Updated sample code for the following messages:ConvertSalesOrderToInvoice  

RetrieveBusinessHierarchyBusinessUnit

QueryExpression
Dynamic Entity Targets Bug fixes in the Dynamic Entity sample code.
Finding the ID of an Entity Instance Added new topic describing multiple ways to find the entity instance ID of a record for use in SDK methods and messages.
Helper Code for ISVs Updated the IsvReadiness sample code:Added new types: OnErrorType, PreCalloutType, PostCalloutType.  

Removed one type: CalloutType.

Added new methods to the CalloutConfigCustomizer class.
How to Work with Lookup Form Controls Added sample code scenario to client side SDK.
Mapping from Version 1.2 Added information regarding the deprecated 1.2 methods for uploading attachments.
Privileges by Message Added the set of privileges required for each message.
Report Development Environment Added information on how to develop reports using a text editor instead of Visual Studio .NET.
Retrieve the Status Codes for Account Added a sample demonstrating how to use the metadata Web service to retrieve the possible status codes for the account entity.
Sample Code Updated the following code samples:Retrieve the Localized State Name  

Route an Incident from a User to a Queue

Added new code samples:

Convert a Dynamic Entity to a Core Entity
Security and Impersonation Expanded the description of impersonation.
Serializing Callouts Changed example code to work around a memory leak in ASP.NET 1.1.
SetStateContract Added information to the SetStateContract message specifying the requirements that must be met to set the state of a contract to Invoiced.
Support for Biz Talk 2004 Added section on support for BizTalk 2004.
Using CRM Attribute Types Updated information regarding the mapping of types from the CRM application to the SDK types. See also Dynamic Entity Classes.
Using Dynamic Entity Bug fixes in the Dynamic Entity sample code.