As discussed here
http://forums.opensymphony.com/thread.jspa?threadID=81984&tstart=0
Compass could find similar objects for a given object, based on term vectors, for example.
I think this makes sense as a CompassQuery, built by CompassQueryBuilder method, eg (pseudo code):
query = CompassQueryBuilder.similar(myObject)
hits = query.hits()
then hits.data is a list of similar objects, ordered by most similar first.
CompassQuery query = session.queryBuilder().moreLikeThis("author", "1").toQuery();