While there are some areas where usability has improved with 8.0 - there are other areas where 8.0 is a significant step backward. While 7.0 had some issues, they were relatively small and few, compared to 8.0 (at least for non-AP functionality).
The usability of interface changes can be easily quantified - measuring the number of screen interactions and the amount of time required to perform operations.
Simple operations in 7.x now take much longer, requiring more screen interactions, and by increasing the amount of time required to do those interactions, it increases the risk of distracting the driver, while the car is in motion. This isn't just a convenience issue - it could be a safety risk.
For example, today I wanted to find a specific NFL game on XM radio. With 7.1, I could use the scroll wheel button to quickly go to XM radio, with one button press bring up the media player window, click to open the "media browser", listing in the XM station categories and quickly get to the list of NFL stations.
That same use case scenario is significantly more complicated with 8.0. You have to click the screen an extra time to even display the app menu bar, then open the media player. Then click on the radio tab - and then the XM button. But there's no easy way to bring up the "browser" list of the XM station categories. It took me 5 minutes (while the car was in motion on the highway) to hunt through the interface - and I eventually did something to bring up the XM radio category list.
There are similar problems in other areas with the user interface.
When I received my P85 in early 2013, Tesla had done a pretty good job in designing a simple and easy to use interface - that also looked great. While it lacked basic features (playlists, waypoints, ...), at least Tesla had implemented a consistent user interface, which was pretty intuitive in how to use it.
8.0 has broken that.
I've been responsible for major software systems - some more complex than the Model S/X software. Our quality assurance teams methodically tested in the user interfaces for those products - and a methodical evaluation of the 8.0 release would show multiple areas where the interface has degraded considerably over 7.0 - and probably would have justified delaying the release so that these user interface problems could be fixed, especially when they potentially impacted mission critical operations (such as driving a car).
We're planning to buy more Tesla cars in the next year or two - and I hope Tesla can quickly fix the problems introduced by 8.0, and take the steps necessary to avoid introducing this many problems in future releases.
