Richard Wiseman ("59 Seconds") describes a lower-cost version of this idea, where you write in response to 5 distinct gratitude-related prompts for 5 consecutive days and repeat every couple of months as desired.

I roughly remember four of the prompts: express gratitude about something, remember and reflect on a past peak experience, write to someone you care about to express how important they are in your life, and think about 3 things that have gone well for you in the past week.