Last year I read his fun book 100 Simple Secrets of Happy People, which has cute anecdotes followed by tidbits of scientific research to back them up.
In my life I've definitely fallen more into the lonely category than the happy one. Both Lonely and 100 Simple Secrets have allowed me to understand why I've felt so bad and so good. That understanding has in turn lead me to have more control, not really over my feelings, but by being able to recognize an incoming bad mood, I can take the needed steps to veer it off its course.
You can listen to the interview I did with David Niven on his book Up! on the archives of the WMNF Evening News.