If you dig into the .ipsw iPod/iPhone software update bundles that are downloaded when you restore of update your iPhone or iPod touch (which are really zip archives in disguise), you can find a file called restore.plist, which is an XML property list stating the various technical specifications of the iPhone/iPod touch model the .ipsw file is intended for. If you look at the "Platform" string under the DeviceMap array in that property list, you'll find a model number of the processor of the iPod touch/iPhone in question, as shown below.
The first-generation iPhone, first-generation iPod touch and the iPhone 3G are all powered by a Samsung S5L8900X series processor, running at 412 MHz, which has been widely documented. The second-generation iPod touch contains a S5L8720X series processor, which is faster than the processor of the three other models that were introduced before it, running at 532 MHz. Meanwhile, the iPhone 3GS contains a S5L8920X series processor, which is widely believed to be based on the Samsung S5PC100 series processor, which itself is a member of the ARM Cortex-A8 family. Apple states the 3GS is "up to 2X faster" than then the iPhone 3G; this is a consequence, to a large degree, of the improved performance of the S5L8920X processor, which runs at 600 MHZ.
The newly introduced third-generation iPod touch contains a S5L8922X series processor, which is a slight numerical increment over the processor in the iPhone 3GS. Also, as revealed in the teardown by iFixit, the model number etched on the processor in the new iPod touch, 339S0075 ARM, also shows a slight numerical increment of the 3GS processor, which is 339S0073 ARM.
Meanwhile, the new iPod touch also shows a increase in the model identifier to iPod3,1, up from iPod2,1 on the second-generation iPod touch. An increase in the first digit of the model identifier usually indicates a major architectural change in the device. For example, the model identifier of the iPhone 3G is iPhone1,2, up from iPhone1,1, as both devices use the same S5L8900X processor.
These signs mostly likely point to some sort of small revision in the processor in the new iPod touch over the iPhone 3GS, however, it's still unclear what improvements this processor offers, if any.
Did you happen to pick up or use a new iPod touch? Did it feel any faster than the 3GS to you? Let us know in the comments below and tell us what you've noticed!