Does iTunes consider a one-star rating worse than no rating at all? If I want to tell iTunes I don't really like a track very much (but don't want to uncheck the track or delete it from my library) should I rate it as one star or leave it with no stars? Which would iTunes consider to be the lesser rating for a track?
No stars is a lesser rating than one star.  This can be verified by sorting a playlist by rating, and having at least one song on it with one star, and at least one with no stars.  The one with one star will float above the one(s) with none.