Apple use misleading name for their iMac GPU, such as talking about Radeon 2600 Pro for underclocked Radeon 2600 XT, leading to some judgement errors, often trying to hide slower and cheaper GPU than actually integrated 
The old generation iMac has a “Geforce 8800 GS” option, a 8800 GS has 96 processors at 550/1375Mhz, and 384MB ram at 800Mhz with a 192bits interface (nvidia spec for the Geforce 8800GS), and in fact it is a “GeForce 8800M GTS”, that sport 64processors at 500/1250Mhz, up to 512MB RAM at 800Mhz with 256bits interface (nVidia’s official specs). Something that is 30% to 40% slower!!!
The new iMac has officially a “GT130″, with 48 processor cores at 500/1250Mhz, and up to 768MB RAM at 500Mhz with 192bits interface. (Official nVidia Specs here). Notice that memory bandwith is in the level of a GeForce 8600 GT!
In fact the new iMac end-up with a “GeForce 9800M GS”, with 64 processor cores, 256bits memory interface and is given twice the memory speed of the GT130, so it’s probably around 800Mhz. (nVidia official page) Good news finally!
So, the new iMac may be not so bad with it’s 9800M GS, that is equivalent to a desktop Geforce 9600, and probably on the same range of performance as the old iMac.
General, Hardware, iMac
GeForce 8800GS, GeForce 8800M GTS, Geforce 9800M GS, gpu, GT130, iMac
Internet was desined originally by the US Army to enable communication between their own data centers, using a distributed network that could not be broken using redondant & alternate routes anytime to stay alive even in case of nuclear attack on the US! Great design!
In the 60’s Internet was open to research facilitis and then some universities research laboratories, to enable fast communication among the US research center. Great move, research is for me at the heart of a nation future!
Now, Internet is used by anyone, anywhere in the world, and this network that was conceived as kinda war room of the future in mid 20th century is now the war room of today:
Chinese attackers try to hack each and every day US Data centers and US facilities, as well as other countries defense systems, Russian atackers had successfully attacked other countries to retaliate, and many corporation are hacking others to obtains IP secrets.
The Internet was conceived as a virtual war room for US Army, but now, the war is on the Internet, every day, and even if it’s a “virtual” war, it could generate threat in the real world.
General
The MacPro has been renewed and now support the Nehalem Xeon processor, but instead of offering more at the same tag price, Apple decided to offer less at the same tag price!!!
The entry-level is now $2899 in Canada with 2.66Ghz x 4-core (8 threads), instead of $2799 for 2.8Ghz x 8-core that is faster in any condition, and the new 8-core begins at $3299 ($500 higher) while being slower than the old 8-core (priced at $2799!), this is just more expansive, and if you want to have better performance than older 8-core 2.8Ghz system, you have to go to 2.66Ghz 8-core priced at $4699, a $1900 premium!!!
Next is the graphic card, a GeForce GT120, that is just the old GeForce 8600GT in disguise, a card that is expected in $500 media center, but not on a $3000+ computer!
Where’s CUDA and OpenCL with such under-powered GPU???
Desktop, Hardware, Mac Pro
Apple decided to downgrade the GPU of the iMac from Radeon 2400/2600 to an integrated chipset GPU that is slower, don’t upgrade the CPU to quad-core (such as any challenging computer), but added a little RAM and bigger hard-drive.
It disappoint me, because Apple upgraded the CPU power of the MacPro (Nehalem), and talk about GPU power using CUDA or OpenCL that will be natively supported in Snow Leopard.
The new iMac offer low GPU power in low-end, and approximately the same average performance level as the last generation while costing more, in high-end! And PC offers from 2X to 6X GPU performance-level at these prices!
The CPU itself is no faster than laptop CPU, than Apple’s laptop CPU, because even high-end laptop offers quad-core these days! The new iMac is underpowered 
Desktop, Hardware, iMac
At least the new Mac Mini, that is the only real upgrade on the new Mac desktop line, and probably the only one that is better than is predecessor:
Apple changed the GPU from GMA950 (Integrated Intel) to GeForce 9400 (Integrated nVidia) that offers full HD output and move capability, and the ability to play old games on low res.
Processors stays almost identical, RAM changed from DDR2 to DDR3 without any real-world performance gain (you will see the tag price difference 
) and enable to upgrade to 4GB instead 3.3GB before, the low-end offers a SuperDrive (at least) and the biggest a 320GB hard-drive.
Nothing astonishing, but more Mac for your money!
Hardware, Mac Mini