I actually do it algorithmically - multiply the rating on each track by their length, add up the answers, and then divide by the sum of the lengths (or you could simply average track ratings and ignore length I guess).

You can probably do this directly on the MM database, Iffin you happen to have MS Access installed on your PC (probably not many people). I used a text export, re-imported into Excel.

Should not be hard to build it into MM, along with the automatic calculation from track data (and, if you like, manual override).

I currently use "Custom 1" but think it it would be handy if MM handled it so that I could use my custom fields for other things.

I've wanted this for the longest time.

Wan't to have the possibility of rating albums