I thought this article about the National Shrine's sound system was interesting.  Something I will argue for is getting away from the use of carpet in the church.  In our church, only a dozen years ago or so, some very nice wool carpet from England was installed throughout the sanctuary and nave.  It was installed incorrectly, though, and is going to need to be replaced with something else soon.  It replaced some other carpeting that had been in for who knows how long... my mom has dim memories of tiles on the floor (not ceramic or marble but something else... asbestos maybe).  One of the reasons I believe churches started going with carpeting was to deaden the echo to make it easier to hear what came through the microphone from the ambo, cantor's mic, and now-a-days, from the priest's body mic as well.  

Carpet worked very well in this application.  However, there was a serious casualty, namely the acoustics favorable for good music.  Now one might say for all these years there was not such good music that you needed great acoustics, or that the answer to improving the sound of the music is to have a fancy sound system installed (that is the route our parish went).  But for one thing, our music director is not fond of using the sound system for the choir, and mic-ing the choir with the organ pipes right there is tricky.  I feel like we need to sing at the top of our lungs pretty much all the time just to be heard downstairs, and I just learned that people down there can't understand the words we're singing, even enough to tell whether we were singing in Latin and English.  I think we need to get back to natural acoustics, so we won't have to shout when we sing to be heard downstairs, and so when we sing beautiful Gregorian chant or polyphony, the echo can become part of the music as it was meant to be.  That means the carpet needs to go.

But what about the problem of the microphones and the speakers' words being garbled by the echo?  That is why I found this article on the sound system at the National Shrine so interesting.  The big upper church has a 6 second echo, and they were able to deal with the problem through the technology of the sound system.  The budget for the whole project was $175,000, which doesn't seem that bad for what they accomplished. 

It's just something to keep in mind when you come up against the argument that "echoes in church are bad" when you propose a beautiful inlayed wood floor or marble floor for your building.  It is possible with sound technology to have both great natural acoustics and intelligible sound from the microphones.