It's not just about web or mobile, it's about web and mobile and even more: build enterprise-class solutions that need performance, high levels of security and scalability.
This page states major improvements in these areas.
Applications that use the built-in GeneXus Access Manager (GAM) now support Single Sign On and are Identity Providers.
GAM has been upgraded to 3.0.6 version: GAM database version 3.0.6.
GAM libraries can generate trace, in order to help trouble shooting: HowTo: Generate GAM trace.
Cryptography data types
GXflow's Inbox is now customizable: GXflow Standard Client Customization.
Processes can be completely Mobile: GXflow - Support for calling native Smart Device applications.
An independent Data Store can be used for GXflow applications: GXflow Support for Independent DataStore.
Support for Dynamic Forms: GXflow Support for Dynamic Forms.
As of GeneXus X Evolution 3, the concept of Buissines Intelligence changes to Reporting. For more information see Reporting in GeneXus
Regular Expressions in the Database Server
Reorganization that converts descriptions attributes in new tables
Redundant Attributes and Nulls
File data type: Text file handling
There are also some other improvements specific to the GeneXus code Generators and their supported platforms
No Evolution 3 specific features have been added to GeneXus Visual FoxPro Generator, iSeries (RPG and Cobol) Generators and .NET Mobile Generator.