In the absence of anything close to Apple's "System Profiler" on Linux, I often look at /proc/cpuinfo for some of the basics. One thing to watch for on AMD CPUs is that the processor frequency (the "cpu MHz" line) in there tells you the current frequency. On an idle system, this is likely to be the lowest of the CPU's available frequencies rather than the "maximum" frequency (the one you were probably expecting to see; "the one on the box").
For example, a 2.2GHz AMD system might report this in /proc/cpuinfo:
cpu MHz : 1000.000
You can find the full details in the /sys file system. The figure you were probably expecting to see is available thus:
$ cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq
The complete list of available frequencies is available thus:
$ cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
2200000 2000000 1800000 1000000
Although the current frequency is an equally valid interpretation of "cpu MHz" as my assumption of the maximum frequency, personally I'd have been tempted to just replace the field with a different one for frequency-scaled processors, along the lines of scaling_available_frequencies in /sys, but perhaps with the current frequency listed first. That at least would be a strong clue to the reader that there's something special about this machine.
A warm reboot doesn't reset everything
Another interesting fact is that, at least with some Linux distributions and some BIOSes, this scaling seems to survive a warm reboot. (I don't actually know what power-saving measure it is that survives, but this would be an obvious candidate.)
If you're using the BIOS' CPU temperature display to see how hot your processor runs when idle, as I was recently, you may well get very different results when you power on and go straight into the BIOS compared to when you boot, tell your OS to reboot, and then go into the BIOS. On one machine I played with, the difference was that going straight into the BIOS made the processor close to 20C hotter.
As an alternative measure of the difference, the difference in the computer's power consumption measured at the wall socket was about 40W, from 145W when going straight into the BIOS down to 108W when going via the OS.
(Interestingly, Linux itself takes less still when idle; around 97W. Even switched off, the machine uses 1.5W. I remember when that would have been enough to run a computer! I'd be curious to see how this compares with other OSes, but I won't buy Windows, can't legally run Mac OS on AMD, and am too lazy to install Solaris again.)