In an attempt to curb the high battery usage of my thinkpad x60, I added a script to each of /etc/acpi/ac.d and /etc/acpi/battery.d to call "cpufreq-set -g performance" and "cpufreq-set -g powersave" respectively.

Are there any downsides to doing this every time the ac is unplugged and plugged back in and so immediately? I've heard spinning your hard drive up and down degrades it and I'm wondering if changing governors degrades the processor or if the governor scales the frequency up slowly to avoid this, etc. Also is this the right way to do something like this? And can I expect my battery life to increase from an hour and a half to something closer to the 4 hours claimed by manufacturer?

I don't think there are any downsides. In fact, those processors are built to scale.
Although I can see one quirk in your choice of governors. On AC power in some cases you could overheat (or to be more precise, reach critical temperature) your processor after long time of 100% usage. If your notebook has a fast processor and inadequate cooling system, as performance governor always runs the CPU at maximum available frequency. I personally prefer conservative governor, which scales frequency one step at a time although some say, that ondemand is better (http://www.bughost.org/pipermail/pow...ay/000071.html) as far as energy efficiency goes.

Thanks for the info, I'll maybe start using ondemand.

But actually it may be too late. I hadn't rebooted in a while and did so last night and checking /proc/cpuinfo today reveals 1st of the Intel Core 2 CPU processors with 4049.49 bogomips and the 2nd with 3990.02 bogomips! Why would they be different? I'm pretty certain yesterday these were both 3995. Anyone know what would cause this?