One of my wife's relatives is a hairstylist. At a family outing last year, we compared notes. She gets requests for free haircuts from friends and family, just like I get requests for free IT services. She finally had to set a policy: no freebies while she was at work (they actually tried this), and no freebies after hours unless you asked nicely and in advance. A gratuity for her time and trouble (babysitting, for example) is A Good Thing.
My policy is similar. I answer e-mails pretty quickly, but everything else is at my convenience. My mother-in-law routinely has a batch of cookies or something similar waiting whenever she needs me to do something. Now, if I just figure out some more things she needs me to do...
When I was still in University I was asked more frequently. Since then I've made it clear where my area of expertise is. It takes some people a while to understand that. And I absolutely will not touch hardware (except a keyboard and mouse) at all. (I have a tendency to fry components because I seem to build up a lot of static electricity that discharges at the most inappropriate moments)
"You can have everything in life you want if you will just help enough other people get what they want." --Zig Ziglar