I wrote about Zip compression yesterday. This interactive essay uses the compressablity (using Lempel-Ziv compression, which is also used in Zip compression) of a song's lyrics as a measure of how repetitive the lyrics are.
The author uses this to understand if songs have gotten more repetitive recently. The short answer: yes, the average song's lyrics are more repetitive now. Rihanna tops the list with an astounding 65% avg. repetition – i.e. compression reduces the size of her lyrics by 65% by removing repetition.