score:5
From my service/experience in the Archdiocese of Atlanta I have observed that, like the CCC states, triple immersion is preferred, but the pouring of water 3 times is much more common.
The variables that determine how each parish baptizes its members are numerous and overlapping, but usually can be lumped into several main categorical reasons.
See http://www.youtube.com/watch?v=EC-w4k7TgCU
You can see a picture of our baptismal font here: http://saintkatharine.wix.com/trenton#!services/c24jx
6 years ago we purchased an old Methodist church building from the Dade County Historical Society and modified its structure to house our liturgies. It was 101 years old at the time, and had no means of performing baptism by immersion. It was only possible within our parish's budget to buy a baptismal font - which leads me to my next reason.
There are countless other factors that determine how a local parish baptizes its members. From apostolic times until now, the Church has faithfully baptized all walks of life from all corners of the world in every generation. This is why the various forms of baptism have been adapted and permitted, while maintaining the true matter and form that is required.
Upvote:4
While I admittedly don't have a book citation for this, my experience (I've also worked as a cantor and have volunteered in different roles in a few different parishes and I've had three kids baptized) is that pouring is the norm. In addition to my experience of the actual rite, I will also point out that most baptismal fonts are simply too small for immersing even the smallest of infants.
I have no idea, however, if this is the case in the third world.