As the Discogs site now displays small icons - green for collection and red for wantlist - right after each release on both the artist and label pages for every user (this was part of the features for an Advanced Account: http://www.discogs.com/help/forums/topic/140251 ), I think this script is irrelevant and useless.

Moreover, as it makes a lot of XML HTTP Request (number of the releases per page... can be very high!!), it may particularly slow down your computer and/or your internet connection.