While there is still work ahead on optimizing the Unity desktop environment, the power consumption while idling at the desktop really has not changed much since early 2011 for this Sandy Bridge system. The Intel Core i7 3960X system with Radeon HD 4650 graphics was idling at about 87 Watts from Ubuntu 11.04 through the recent Ubuntu 12.10 development snapshot.
With OpenArena's performance there was a jump in performance for Ubuntu 11.10 on the Radeon HD 4650 that I do not believe has been documented previously. Unfortunately this jump in performance has receded since with the more recent Mesa / Linux kernel / xf86-video-ati packages. Aside from Ubuntu 11.10 being faster, the other three releases all performed about the same speed.
Ubuntu 11.10 was burning through noticeably more power though when its performance was up, but when it comes to performance-per-Watt the numbers were similar.