Some of the enhancements are:
- Cleaner Markup: The Microsoft SharePoint Foundation (MSF) controls are no longer table based, and all the CSS classes were re-factored and cleaned up.
- SharePoint 2010 is XHTML compliant, and also supports WCAG 2.0.
- Reduced Postbacks / Page refreshes.
- Server Ribbon, which copies the functionality of the ribbon in Office applications.