there used to be a site for benchmarks:
http://homepage.mac.com/breadboi/shake
which apparently is out of bandwith atm 
for those interested, i did a quick benchmark with the following script (which should be not i/o limited)...
CODE
// Input nodes
Checker1 = Checker(720, 576, 1, 32, xSize/GetDefaultAspect());
Grad1 = Grad(2048, 1556, 1, 0.5, 0.5, 1, 0, 0, 1, 0, 0, 1, 0,
1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0);
// Processing nodes
FilmGrain1 = FilmGrain(Grad1, "v3.0", 1, 1, 1, time, "Custom",
0.05, rStdDev, rStdDev, 1.2, rSoftness, rSoftness, 0, rFilmResponse,
rFilmResponse, 0, 0, 0, 0);
Resize1 = Resize(Checker1, 2048, 1556, "default", 0);
Primatte_v21 = Primatte_v2(FilmGrain1, 0, 0, 0, 0, 0, 2, 0, 0, 0,
0, "a", "a", 0, 0.5, 0.5, 0.5, 1, 1, 0, 0, 1, "80000WDcsuyUNVK40KXr2cAWDA0000014");
KeyMix1 = KeyMix(Resize1, FilmGrain1, Primatte_v21, 1, "A", 100,
0);
Resize2 = Resize(KeyMix1, 720, 576, "default", 0);
benchmarks = FileOut(Resize2, "/Volumes/RAID/benchmark/benchmarks.#.jpg",
"Auto", "rgb", 100);
on a mac pro 2.66 with 1GB ram...
interesting results:
macpro:~ chris$ shake -v -cpus 4 -exec /Volumes/RAID/benchmark/benchmark1.shk -t 1-100
info: rendering frame 1
info: frame 1 rendered in 1.95s
info: rendering frame 2
info: frame 2 rendered in 1.92s
info: rendering frame 3
info: frame 3 rendered in 1.95s
info: rendering frame 4
info: frame 4 rendered in 1.93s
info: rendering frame 5
...
macpro:~ chris$ shake -v -cpus 2 -exec /Volumes/RAID/benchmark/benchmark1.shk -t 1-100
info: rendering frame 1
info: frame 1 rendered in 1.47s
info: rendering frame 2
info: frame 2 rendered in 1.41s
info: rendering frame 3
info: frame 3 rendered in 1.79s
info: rendering frame 4
info: frame 4 rendered in 1.84s
info: rendering frame 5
info: frame 5 rendered in 1.81s
info: rendering frame 6
info: frame 6 rendered in 1.79s
info: rendering frame 7
..
macpro:~ chris$ shake -v -cpus 1 -exec /Volumes/RAID/benchmark/benchmark1.shk -t 1-100
info: rendering frame 1
info: frame 1 rendered in 1.88s
info: rendering frame 2
info: frame 2 rendered in 1.87s
info: rendering frame 3
info: frame 3 rendered in 1.87s
info: rendering frame 4
info: frame 4 rendered in 2.04s
info: rendering frame 5
info: frame 5 rendered in 1.86s
info: rendering frame 6
info: frame 6 rendered in 1.87s
info: rendering frame 7
strangely enough, the 2 CPU setting was a bit faster than the 4 cup setting ..
i did check the activity monitor and the CPUs did in fact recognize the cpu 2 and cpu 1 option, but switched between processors for each frame.
would be interested in the results on a quad g5
++ christoph ++