Of course I don't use cronjob for everything. Clock and mpd info go through system calls and libmpd respectively. If I were doing the CPU/temp/etc things (in which I have no interest), I'd probably also just get those through system libraries as well (assuming I'd want them every update).
The temp file is only for the title of a radio program that I can't get other than scraping it from a website (no metadata in the stream ...). It only changes once an hour (max), so I need to store it somewhere.
I've hacked my bar together in C though, so things may be slightly different.