Microsoft commissioned Principled Technologies to help them silence the complaints about Vista performance. Principled Technologies complied:

We have produced the following currently publicly available report for Microsoft Corp.

Responsiveness of Windows Vista, Windows Vista SP1, and Windows XP on common home tasks We measured the responsiveness of three operating systems—Windows Vista, Windows Vista SP1, and Windows XP, when performing a set of common home tasks after rebooting, returning from standby, and in ongoing operation. We tested five systems: Dell XPS 600 (desktop), Dell XPS M170 (notebook), HP a1320y (desktop), HP d4100e (desktop), and Toshiba Tecra M4 (tablet).

Responsiveness of Windows Vista, Windows Vista SP1, and Windows XP on common office tasks We measured the responsiveness of three operating systems—Windows Vista, Windows Vista SP1, and Windows XP, when performing a set of common office tasks after rebooting, returning from standby, and in ongoing operation. We tested five systems: Dell XPS 600 (desktop), Dell XPS M170 (notebook), HP a1320y (desktop), HP d4100e (desktop), and Toshiba Tecra M4 (tablet).

Responsiveness of Windows Vista and Windows XP on common home tasks (2007) We measured the responsiveness of two operating systems, Windows Vista and Windows XP, when performing a set of common home tasks after rebooting, returning from standby, and in ongoing operation. We tested five systems: Dell XPS 600 (desktop), Dell XPS M170 (notebook), HP a1320y (desktop), HP d4100e (desktop), and Toshiba Tecra M4 (tablet).

The impact of switching from Windows XP to Windows Vista on common business task efficiency (2007) We explored the response time a typical business user would experience during real-world work scenarios on Windows Vista and Windows XP. We measured responsiveness on a range of systems after rebooting, returning from standby, and in ongoing operation.

My take on this? Performance benchmarks are bogus, and new OSes are always slower than their predecessors on the same hardware. So what? In day to day use, I find Vista's performance to be just fine, thank you very much, and I'd never consider going back to an older OS for some perceived but largely illusionary performance bump. Vista offers better security and functionality than XP, and there's just no turning back.

In any event, if you download the above linked reports (the first two are new while the next two are from last year), you'll discover, surprise surprise, that "overall, Windows Vista SP1 and Windows XP performed comparably on most test operations [but] Windows Vista SP1 was notably more responsive after rebooting than Windows XP on several common home operations." This was true for both common home and business tasks.

Gentlemen, start your complaining. :)