Note, that is different from geek hobbies. :-) Steve talked about techies having non-technical hobbies. This reminded me of a job I interviewed for a few years ago (in marketing - long story, basically I was tired of the death march to RTM  and wanted to do something more customer-centric for a change).
In that loop, two different interviewers during the day asked me what my dream job was. Being naive, I answered honestly to both: to be a photographer. It's hardly a secret. My office door is literally covered floor to ceiling with 8.5x11 and larger printouts of my photos, and they spread out to the walls outside my office as well. Most of them are in our home studio, so they're not the snapshot variety of photo. I have so many pictures of my son on display that people who walk by often think I have more than one kid. People who walk by regularly stop to talk to me about photography.
I got to the end of the interview loop, even passed the 'as appropriate' interview from what I could tell, but the hiring manager asked to meet with me again. He told me that I did great in the loop, but he got feedback that I didn't seem to want to be at Microsoft and that was the reason he wasn't going to offer me the position.
I went on and got another job instead (that was more technical and still more customer-centric than my previous job) and in retrospect, I made the exact right choice for me at the time. But looking back on it now, I just have to laugh, because it's so similar to something that happened to me very early on in my Microsoft career. When I was interviewing for my first-ever full-time job, I got the job, but found out a few years later that I got all hires and one no-hire. The woman who gave me a no-hire felt that I did great on the actual testing part of the interview, but when she asked me about why I wanted to work at Microsoft, my answer was closer to the "free pop" end of the scale instead of the "making a difference in people's lives by working on software used by millions of people all over the world" end. What can I say, I was 20 years old and the whole idea of having my own office (and free pop) was pretty cool. I had never even had my own apartment.
I really love getting to know my coworkers well enough to know what their hobbies are, and I find the non-geek hobbies much more interesting than the geek ones. One of the testers on the Exchange team does emergency search & rescue. If someone goes missing, he may be called in to help sweep the area. IIRC, he has a story about "finding a hand." (Eep!) Several devs and testers on the team biked the STP this past year and raised thousands of dollars from the rest of the team for a charity. Over the years I've seen many people who pour their freetime into acting, kayaking... we've had artists, wine collectors, an ironman, a member of the Falling Illini skydiving club...
I took an interviewing course last year and I told the story about that interview question, and the teacher said "What an awful interview question! The only right answer to that is 'this job'!" I totally agree, and I never ask that type of question when I interview. I like seeing multiple sides of a person inside and out of an interview, or seeing how passion and expertise at work spills over into hobbies, such as with some of my coworkers that donate their time to install and maintain Exchange servers at local non-profits and religious centers. I love photography, I'd love to be able to make a career out of it, and if I really thought I had a shot at being the next Anne Geddes or Robert Doisneau, you bet I'd quit and pursue that. But back here in the real world, does having a passion for a hobby mean that I wouldn't be a great employee? Of course not. And if letting that passion shine through ever keeps me from getting a job I want (and sure, that might happen some day), then oh well. I think many people have these types of dreams and finding ways to pursue those dreams alongside our day jobs is just part of trying to achieve work-life balance... which isn't easy; more on that later.
 Ironic, isn't it, since I'm now in charge of leading the march. ;-)
 P.S. when trying to find out more about what equipment someone uses to create something, try and throw in a compliment that makes clear you appreciate the skillz behind that creation. You would never compliment someone who cooked you a great meal by skipping right to asking them what pots they would use, would you? For photographers, "You've got a great eye." is an innocent and always welcome compliment, even if it is immediately followed by "...incidentally, what camera/printer/lens/filter/tripod/software do you use?" :-)
 In the as-ap (for a marketing job mind you) with the general manager, the first question he asked me was about a sorting algorithm. I was so dumbfounded that I stammered for like 40 seconds, and then finally (slowly, painfully, sweaty-palms-y) worked it out on the board. I was mortified at myself for being so thrown off by that question, but I just wasn't expecting anything that technical. It just goes to show you, you had better be prepared for whatever gets flung at you.
having interests and hobbies outside of your main job is what keeps you sane and allows you to develop a more rounded personality.
personally I would be more hesitant over the candidate who only has hobbies that are the same as their job - sure it depends on the role but certainly in customer facing roles, if all you can talk about is how the .NET CLR works, thats not going to be very useful.