I also found it interesting that participants had a strong emotional connection to the 2.5 admin interface even when the formal usability metrics proved that they had trouble using it! Apparently good graphic design (my attraction to the UI) helps to mitigate formal usability flaws–a point worth remembering.
Jane Wells at WordPress opens the kimono further on the decision to redesign the administrative user interface for 2.7. I griped a while back that it seemed like the design changes were being made in a non-systematic way, but it turns out there were solid usability testing exercises prior to the surveys we’ve all seen about structuring the navigation menu. She also includes a detailed usability report covering the eye tracking studies and the different stages of the process. Sounds like the new administrative screen is genuinely a usability improvement in terms of the metrics that matter (task success and time on task).