First, Android 2.0 bakes in native Exchange support for corporate email. That's good news. It also incorporates Facebook into the contacts applications and will sync Facebook directly with the phone. There's also a unified inbox for messaging, browser updates and a new Google Maps program.
According to The Boy Genius's test device, the unified inbox holds most emails, but not Gmail, which still uses the separate on-board Gmail client. It appears as though batch processes are supported, such as manipulating multiple messages at once.
Maps has been improved to support layers, such as traffic, and other information such as transit systems, and Latitude friends. The browser has a revamped user interface, which includes better URL entry. There's a new mode called "Car Home", which simplifies the user interface for use in a moving vehicle (hopefully with voice commands and not your finger).
The contact program has seen some updates, including new submenus for taking action (such as placing calls or sending messages) from the contacts page.
In all, it is a lot to look forward to. No one knows if Android 2.0 is Eclair, but I've heard from at least one handset maker that Eclair is really something to look forward to.