Surely you should just ignore their request, then? I the occasional request like that but just ignore it. I actually have added friends regardless of what field they're in. In fact you might be missing out since they may be able to help you get insider access to other companies, even if they're programmers themselves. Or, you may be able to help them out. Basically, I added anyone I would feel comfortable asking to forward a resume for me (or someone else in my network). That's a high proportiion of people I've worked with closely, but not everyone.
One of my former colleages asked me to forward a resume for a collegue of his, the classic 'friend of a friend' thing. Since I trusted his judgement, I felt comfortable doing so. Another friend has recently graduated college, so I told her to look through my network and let me know who she'd be interested in talking to as she decides how / where to start her career, and then made the introductions (after asking my connections if it was ok, of course)
I check in every couple of weeks - I get the profile change updates and will occasionally send messages to people in my network if I see something interesting that they've done.
Basically, I'm trying to build up my karma so than when I next am looking for a job I'll it'll come back around
HOLY MACRO!