According to The Daily Mail (that highly reputable news source), when dogs chase their tails, they're doing something which is similar to ritualistic behaviour in humans. The same dogs who are habitual tail-chasers are also more likely to be startled by loud noises and timid in their general behaviour.
Although this is 'fascinating fact' sort of stuff, it does seem to be quite useful in others ways - scientists are able to examine the behaviour of dogs and whether differences in breed, gender, upbringing and diet have an effect on the behaviour the dogs display. The plan is then to investigate whether this translates into human behaviour, giving researchers an insight into the development and treatment of Obsessive Compulsive Disorder in people.
One of the emergent theories is that dogs are more likely to develop anxious, compulsive behaviour if they've been separated from their mothers early in their lives. This, for me, makes a lot of sense: I've always found that my OCD is worse when I'm separated from my Mum, and one of my main anxiety triggers is being on holiday away from my home and family. Although my family can leave me in the house alone and I seem not to have a problem with that. Maybe with dogs and people it's a lack of routine which triggers obsessions and compulsions in people who are predisposed to anxiety disorders?
On another note, it really annoys me how the Mail lists stepping on the cracks in pavements (or not depending on which way you swing!) as a 'mild symptom'. Obviously the author's never walked down a road with crazy paving...