i believe that the document labeling system involved the metadata structure of the origional mac os that apple kind of snubed for osx. however, apps can still take advantage of the metadata (thank goodness, suffixes are ugly and dare i say dos-like) and i believe that there was some kind of launcher utility (it may be dragthing, but i'm not sure) that allows you to view (not apply unfortunately) labels from your files. i dont think that it would be too hard to incorporate this into osx and some clever hackers could probably figure out how to edit some of the finder's files to allow it. apple may re-introduce it later on, just look at springloaded folders, people complained until they came back.