There are few improvements, the major improvement is the portal (PortalHomePage) which is ASP.NET with Ajax and now you have CSS and XML for strings.
You can read the Forefront UAG customization guide: http://technet.microsoft.com/en-us/library/ee861168.aspx
The following topics describe:
- Customizing the portal—The customizations you can make to the Forefront UAG portal to modify the look and feel as well as some of the functionality.
- Customizing the InternalSite—The customizations you can make to the Web application (also known as the InternalSite); for example, modifying text or the login and logoff pages.
- Customizing the detection module—How to modify the detection module, which identifies the type of device connecting to the portal and presents the correct portal pages.
- Customizing endpoint components—How to create a custom script to detect applications on client endpoint devices, and how to modify which endpoint components are downloaded to client devices.
- Manipulating HTTP responses with AppWrap—How to use the Application Wrapper (AppWrap) configuration file to manipulate HTTP responses from backend Web servers to end user client devices; for example, removing the logoff button from applications published in the portal.
- Customizing the Web Monitor—How to customize the Web Monitor; for example, modifying the layout of charts displayed in Web Monitor, or modifying the user interface presented to the end user.