I'm pretty sure you're talking about The Year of Living Bibilically by A.J. Jacobs. I used to listen to the audiobook version of this all the time.

My other favorite of his was The Know-It-All, where he read the encyclopedia from beginning to end to increase his knowledge.

One of the interesting things that he revealed was that he has a tiny touch of OCD so the rituals helped him to take his focus off his OCD. The religious rituals behaved as a ritualistic substitution for his OCD at times. One thing I'm curious about is how he picked the things he prayed about. Was he grateful the car started on a brand new car? Did he pray that his computer started? Did he pray that his chair didn't break when he sat on it? Did he pray that he got up without a sickness? How likely was the thing that didn't happen? There are thousands (or limited only by the imagination really) of things that don't go wrong every day. Taken to an extreme, thinking about them all can get one pretty paranoid. How does one choose?

There's more research on the impact of gratitude on happiness. Here is some research by the positive psychologists in a Harvard article. There are other ways to express gratitude as well as prayers. Some of the other ways are thanking people (both outwardly and inwardly), counting blessings and meditating.

I've started a blog several months ago to write a positive thing every day to help focus me on things I'm grateful for. Before that, I kept a gratitude journal where I wrote 3 things I'm grateful for every evening for 2 years.

Edit: I read the Harvard article more carefully and this part made me laugh out loud.

There are some notable exceptions to the generally positive results in research on gratitude. One study found that middle-aged divorced women who kept gratitude journals were no more satisfied with their lives than those who did not. Another study found that children and adolescents who wrote and delivered a thank-you letter to someone who made a difference in their lives may have made the other person happier — but did not improve their own well-being. This finding suggests that gratitude is an attainment associated with emotional maturity.

Either this is written really poorly or they're implying that middle-aged divorced women are emotionally immature.

Edit 2: If you like experiments in happiness, you might like Gretchen Rubin's website My experiment in the pursuit of happiness or her book The Happiness Project taken from her website where she experiments on herself with some of the happiness wisdom of the ages.