Over on the Catholic Answers Forum, I started an interesting thread on why guitar-based praise and worship music, such as "Shout to the Lord" or "Days of Elijah," shouldn't be used at Mass. I tried to get posters to go beyond a simple "I don't like it."
I learned a lot, and I was made aware of certain Vatican documents that seem to have been either ignored or watered down. But there do appear to be loopholes. Anyway, the consensus appears to be that such music may well be appropriate for prayer meetings, but not for the sacrifice of the Mass.
Here's a relevant quote from Tra le Sollecitudini:
VI. Organ and instrumentsI think this goes to show how much I conflated the community gatherings we had in Lamb of God with the Mass, and how the former had become more important to me than the latter. At the community gatherings, it was all praise and worship, all the time.
15. Although the music proper to the Church is purely vocal music, music with the accompaniment of the organ is also permitted. In some special cases, within due limits and with proper safeguards, other instruments may be allowed, but never without the special permission of the Ordinary, according to prescriptions of the Caeremoniale Episcoporum.
16. As the singing should always have the principal place, the organ or other instruments should merely sustain and never oppress it.
17. It is not permitted to have the chant preceded by long preludes or to interrupt it with intermezzo pieces.
18. The sound of the organ as an accompaniment to the chant in preludes, interludes, and the like must be not only governed by the special nature of the instrument, but must participate in all the qualities proper to sacred music as above enumerated.
19. The employment of the piano is forbidden in church, as is also that of noisy or frivolous instruments such as drums, cymbals, bells and the like.
20. It is strictly forbidden to have bands play in church, and only in special cases with the consent of the Ordinary will it be permissible to admit wind instruments, limited in number, judiciously used, and proportioned to the size of the placeprovided the composition and accompaniment be written in grave and suitable style, and conform in all respects to that proper to the organ.
21. In processions outside the church the Ordinary may give permission for a band, provided no profane pieces be executed. It would be desirable in such cases that the band confine itself to accompanying some spiritual canticle sung in Latin or in the vernacular by the singers and the pious associations which take part in the procession.
Now I realize many of you reading this are from other denominations/religions, but I wonder whether your services have had similar arguments over what music to play or not.