PocketNow has tried an early build of HTC Sense 4.0, and says that the latest update reduces the amount of visual clutter seen in Sense 3.5. The update will also add a card-like task switcher, landscape support for the home screen, and an updated email client with Smart Sync, which can predict usage habits to conserve battery life (e.g. no checking for emails at 3AM, unless you are usually a night owl).
Beats Audio will also be open to third party apps, rather than being limited to the default music player. The camera app has also been updated, to eliminate pictures of people blinking (five pictures are taken within milliseconds of one another, the faces are examined, and the best picture is automatically chosen).
There will also be a new guest mode, so that you can let people borrow your phone, and not have to worry about them accessing your private data and apps. Sense 4.0 will have better DropBox integration, with 50GB of free space given to you when you first setup your phone. Apps will treat the 50GB of online storage as if it was another drive on the device.
HTC Sense 4.0 devices will apparently not have on screen keys as found on the Galaxy Nexus, they will instead have a three button configuration, meaning that the search button on HTC devices is going.