Computers can make a lot of heat! Its important to make sure that they do not get too hot, and reducing the heat they generate can reduce the energy used to keep them cool.
I've had some issue monitoring computer temperatures, but here's one way I do it:
smartctl --all /dev/hda | grep Celsius | awk '{print $10}'
I'm now also using RRDTool to store temperatures:
rrdtool update temps.rrd `date +%s`:`cat /proc/acpi/thermal_zone/THRM/temperature | awk '{ print $2 }'`