Some years ago, I've written some Python scripts that automatically populated the the POPM ID3 tag (popularimeter) with "popularity data" from Audioscrobbler and also from the local iTunes media library (using the ratings field). See:
I think something like this would be useful in Jaikoz.
The POPM tag is hardly ever used because most people don't know what it's for. iTunes doesn't use it directly. But automatic rating from some external sources and coordinating this with the iTunes rating would be useful. I for one would love if the songs I import into iTunes were "pre-rated" using some community input. This is why I wrote these scripts. And the POPM tag is a good place to store this info inside an MP3.