Please never consider such characteristics (number of cores or their frequencies) as an advantage when buying any mobile gadgets. Mobile technology varies highly and such characteristics are usually can't be easily compared between different hardware vendors (e.g. two 400mhz GPUs might have completely different performance profile.) I don't know what kind of hardware they have there but it might be anything — from a plenty of slower cores to having many specialized cores. Also a lot depends on software and it's integration with hardware. Do test real devices and measure real-life performance. That's the only way to tell if there is any improvement whatsoever.
I would expand this to say don't just compare speed across brands on PC either- if you compare a quad core Intel to a quad core AMD, you'll see quite a difference. It's all about how those cycles are used!
I wasn't trying to make a baseline strength comparison, I was more curious about where the 12 figure came from. I was under the impression that Tegra 3 was a quad or dual core gpu ( turns out according to http://www.nvidia.com/object/tegra-superchip.html its an 8 core gpu ).
Very different architectures. Anandtech did some performance comparisons of Tegra3 to the new iPad's PowerVR SGX543MP4 which show the PowerVR delivering better performance with "fewer" cores and far lower frequency:
What constitutes a GPU "core" is anything but well defined. Heck, people argue about whether the FX-8150 has 8 or 4 cores, but if we were to use NVidia's methodology we'd probably call it 16 or 32 cores. Who knows how Apple counts "cores" in their GPUs.