You may remember that an Intel executive (one year ago or so) in an interview said that the Internet browsing experience in the iPhone is not that good because an ARM processor is used instead of an Intel Atom. Of course this sentence is a pure provocation since the Atom processors weren't (and still aren't) suitable for handsets: they are too power hungry.
The first iPhones 2G and 3G included a Samsung SoC based on the ARM11 core clocked at about 600MHz, much more power efficient than actual Atoms. On the other hand Atom processors are definetly more powerful than ARM11 processors.
In the past couple of years ARM introduced Cortex A8 and Cortex A9 cores, processors able to reach and potentially beat Intel Atom.
Just to give an example showing how "bad" the ARM11 compared to the new Cortex, I report the peak DMIPS/MHz. It is a clock-per-clock performance indication of the processor (used especially for Marketing purpose)
ARM11 cores and the new ARM Cortex A8 and Cortex A9.
Example of devices using the ARM cores
Apple iPhone 3G uses an ARM11 processor while the iPhone 3GS an ARM Cortex A8.
The ARM Cortex A8 is also used in Qualcom Snapdragon and NXP i.MX515 SoCs.
The first ARM Cortex A9 based SoCs (System on a Chip) are expected in 2010.
Nvidia Tegra 1 is based upon an ARM11 and it's unknown whether or not in Tegra 2 an ARM11 or a Cortex A8 / Cortex A9 will be used.
UPDATE: Nvidia Tegra 2 uses a Cortex A9 MPCore
Unfortunately I didn't find stable benchmarks results for the Cortex A8/A9 processors, stay tuned... A number of netbooks/smartbooks equipped with ARM processors are expected next year (2010).