Recently Christianity Today had some articles on music for the worship service. Notice that if one simply says worship music, it might refer to a contemporary style of music which may or may not be used during a worship service. The article that has given me the most to think about is Pop Goes the Worship. Author T. David Gordon mentions in the interview that music for the worship service should be folk music in the sense the it should be singable by the people, rather than music designed for performance. I grew up singing in a choir, not that I excelled at music, but I learned to love the hymns, though I also like much in the contemporary Christian music. A point that Gordon makes though is that we of sing contemporary Christian music with just words, though it is often more sophisticated and difficult to sing. We sing hymns with notes written out.
Another article about hymns is in on the webzine By Faith Online which discusses Indelible Grace's recent documentary.