The following are the feature new in Windows Mobile 6.5.3....

Ease of Use features

• Capacitive touch screen support
• Platform to enable multi touch
• Touch controls throughout system (no need for stylus)
• Consistent Navigation
• Horizontal scroll bar replaces tabs (think settings>system>about screen)
• Magnifier brings touch support to legacy applications
• Simplified out-of-box experience with fewer steps
• Drag and drop icons on Start Screen

IE Browser Performance

• Page load time decreased
• Memory management improved
• Pan & flick gestures smoothed
• Zoom & rotation speed increased

Quality and Customer Satisfaction features

• Updated runtime tools (.NET CF 3.5, SQL CE 3.1)
• Arabic read/write document support
• Watson (error reporting) improvements and bug fixes

Source: Winsupersite