Or, a modern guide to CPU frequency scaling with Linux. Having
setup my laptop long ago, I had a strange hybrid of daemons running
all trying to scale the frequency of my laptop periodically based on a
myriad of different situations. Having decided to fix this, it
appears the simplest approach is, as usual, the best.

The way of the future appears to be to let the kernel do all the
work with the ondemand govener. The cpufrequtils
Debian package will arrange this for you on boot and by default should
just work, although you can of course tweak parameters like
minimum speed to decrease to and so forth. You can use the
cpufreq-set utility to fiddle with settings, or just go into
/sys/devices/system/cpu/cpuN/cpufreq/ to tweak them by hand.
The many available daemons (cpufreqd, powernowd,
etc.) appear to be largely redundant and are probably best
removed.

This dropped the temperature of my laptop about 10 degrees C and,
apart from a much cooler lap, is so far imperceptible.