Here are my comparison data as I've now downgraded to 10.6.8:
Hardware: MacbookPro3,1 with 6gb RAM and drive is Samsung HM250HI
Tests made in 32bit kernel mode in both cases (CPU is 64bit).
Cinebench OS X 10.7.5: CPU 0.91pts, OpenGL 6.70fps
Cinebench OS X 10.6.8: CPU 0.88pts, OpenGL 6.28fps
Xbench OS X 10.7.5 CPU: 153,06
Xbench OS X 10.6.8 CPU: 150,00
In these tests Lion is faster on all points, though the tests are limited in scope. To me this nevertheless gives some numerical reference to the same experience I've had: that CPU intensive work such as Photoshop filters, Audio calculations and similar isn't slower in Lion. Rather those run a tad faster.
However, the GUI seem somewhat more responsive now in a fresh install of 10.6.8, but I can't tell how it will feel 6 months from now. Unfortunately I didn't run those tests in Lion for time constraints, but if this observation is true, that could be one reason why people would think Lion is slow. If the performance is similar in newer machines then the GUI advantage if any wouldn't be noticable, because it's very little.
I'm willing to entertain ideas for better tests, but I really think most slow Lion stories are myths rather than facts. That said I won't be upgrading to Lion on this machine again. It's Mountain Lion or staying in Snow Leopard.