Well, it looks like Riley does a bit more than shed, chew on cords, and season the furniture … I found this on the web (via slashdot):

The finding, from a 10-year study of more than 4,300 Americans, suggests that the stress relief pets provide humans is heart-healthy.

– US News & World Report : Cats Help Shield Owners From Heart Attack
‘course I knew he made me feel calmer… and I think I found a site that referenced a study that showed cats helped lower blood pressure.