The metadata API service has been extended to retrieve language information in MSCRM4.0.
Multiple organizations can now be hosted and WSDL APIs are now unique per organization in MSCRM4.0.
Plug-ins (callouts) and workflow now use the same event framework, allowing for even more extensibility.
The SDK has been expanded to include offline access.
Now we can programmatically create, read, update and delete the metadata such as entities, attributes and relationship.
There are three services instead of two which we used to have in previous version
Many to Many Relationship was not available in MSCRM3.0
Multicurrency feature was not available in MSCRM3.0