It depends on what your personal interests are. In the current litigious environment, it's not a good idea to mention things that indicate personal situation, e.g., "I love spending time with my three kids." The employer may think you are setting them up for a lawsuit in the event that you are not considered for an interview: "You didn't hire me because you know that I have kids."

However, when your interests can be directly or indirectly used to strengthen your application, add them. For example, if you are looking at a charge role, and you have extracurricular supervisory experience, say over a volunteer ski patrol, say so. Or if you enjoy volunteer work, e.g., as a first aid or CPR instructor, free clinic worker, say so.

And if you have a particularly unique personal interest, like having traveled to five continents, say so!