Recently, a colleague whom I know from my writings and speaking asked me for a reference. I've never seen him work and I explained I could not provide a reference. He was quite angry with me.
In Choose Enough References, I suggest asking people who can explain the value of your work. Let me be more explicit: Do not ask people for references who cannot attest to how you work. Don't do it.
The value of a reference is in the specifics and enthusiasm of the reference. Last night, I gave a reference for a former babysitter who's looking for a live-out nanny position. I was enthusiastic, told stories about how wonderful she was when my children were little, medium, and even as young teenagers, when Mark and I needed to be away overnight. The woman who asked for the reference said I must have said the word “wonderful” at least 200 times. That's the kind of enthusiasm you want to engender in your references.
Ask people for references, and make sure they can attest to the value of your work. Don't ask people who haven't worked with you directly, even if you think having them as a reference would be helpful. Unless you've worked with a VP who was three levels above you, don't ask unless there is some project you worked on with the VP.
Being a reference is an honor and a responsibility. Don't ask someone to take on the responsibility unless you know that person and that person knows your work.