Is cpu-freq intended for laptops or is it useful for desktop systems, too?
I sometimes use vcpufreq with my desktop (an Intel Core 2 Duo).
It only gives me two options (1.6GHz and 1.86Ghz), though, which makes its usability somewhat limited.
I usualy run it in performance, which keeps it at 1.86, but if I see my temperatures going up on a particularly hot day, I might go for ondemand or conservative. Not that the lower frequency makes that much difference.
I find lmsensors (displayed by conky) to be very useful to monitor the current frequency and temperature.
However, the values are slightly different from the BIOS ones... there's also the coretemp module for intel's dual-core cpus (monitoring each core separately), which also gives different temperatures.
I'm not sure about these differences... different sensors, different monitoring.... I came to look at it in a relative sense (relative to some "normal" baseline on colder days), and don't care much about the actual absolute temperatures.