Now, let me give an overview of the paper you mention, titled Counting Blessings versus Burdens: An Experimental Investigation of Gratitude and Subjective Well-Being in Daily Life. The paper includes 3 separate studies, BrainFire so I will just be able to provide a quick glimpse. More than a hundred adults were all asked to keep a journal, and were randomly assigned to 3 different groups. Group A had to write about things they felt grateful about. Group B about things they found annoying, irritating. Group C about things that had had a major impact on them. 2 out of the 3 different experiments were relatively intense and short term (keeping a daily journal for 2-3 weeks), while one required a weekly entry during 10 weeks.http://www.healthcaresup.com/brainfire/