The first feature touted on Android 4.1's official website is that the OS is now "fast & smooth":

With buttery graphics and silky transitions. We put Android under a microscope, making everything feel fast, fluid, and smooth. Moving between home screens and switching between apps is effortless, like turning pages in a book.

Too late, Google. This is a feature Apple shipped with iPhone OS version 1.0 in 2007.

Every opportunity I get, I pick up an Android device and scroll through a large list—sometimes these are contact lists, sometimes they're within the music app on the device. A consistent trend happens when I do this: the device doesn't scroll smoothly. It kills me.

I hope this changes with Android 4.1, for the sake of the users. A laggy interface causes a disconnect between the device and the user. It makes the person using the device aware they're using a device: it breaks the magic of interacting with a touchscreen. When I use my iPhone or iPad, I forget that I'm interacting with a computer—it feels like I'm directly manipulating the content on the screen. Losing this amazing human-computer interface experience is a major problem.

And when there's a problem with an interface, there's a problem with your product. As Jef Raskin famously said:

As far as the customer is concerned, the interface is the product.