Windows iTunes: Where are the lyrics saved to? In iTunes, we can right click a track and do "Get Info" and add some lyrics to the track. 

I have a text file that is roughly 500 kB.

My MP3 file is 3.47 MB. For some reason, when I set the lyrics to the contents of the text file (in other words, roughly half a megabyte), my MP3 file size is still 3.47 MB.

Where are the information for the lyrics saved to?

(Windows Vista 32-bit SP2)
It is entirely possible that you have iTunes set to copy files to its own media folder, in which case the original audio files are not changed.

To find the location of the audio file iTunes is using, look under the "Where:" label in the "Summary" tab.

iTunes (both Windows and Mac) does use the lyrics field in MP3s to store lyrics, and will cause the modification date and time, as well as the size, to change.