Change iTunes to save audio files in MP3 format?

It's a question I hear time and again: I've been ripping music CDs with Apple iTunes and it's been working fine, but now that I have an MP3 player of some sort - a cellphone, MP3 device, iPod or even Sony PSP - all of a sudden I realize that the files are in the wrong format (usually AAC). How do I change iTunes to save the audio files in MP3 format in the first place, rather than worrying about any sort of conversion necessary?

    iTunes saving audio files in MP3 format

It's surprisingly not hard at all once you know where the preferences are stored...