Google announced they have made some design changes as part of their "Google-wide initiative to deliver a simpler, more beautiful experience across all of Google products."
The design changes are not all that significant. The most prominent changes are:
(1) Help section is now moved to the top right and opens up when clicked on. Here is a screen shot:
(2) Performance Reports are now organized by type to make it easier for you to find and understand the reporting. Here is a screen shot:
And overall the design is clearer and more uniform to other Google interfaces.
Here is a full size screen shot that you can click on to see more:
The biggest complaints is that the interface no longer works on iPhone or iOS devices well. Additional complaints are on the ad review center, and some button placement is confusing.
Forum discussion at WebmasterWorld.