Using community volunteers for technical support

I recently spoke to a librarian in Oklahoma whose technical support comes almost entirely from a community volunteer. Other libraries I have spoken to rely on high school interns to provide technical training and support.

She said, "We have a former board member who has been with our library since we started in our technology process. He volunteers and donates his time to do any of our technology projects. He’s wired our building and things like that…we have wonderful donated tech support. He has saved us so much money…I’ve really been blessed with our wonderful board. And we have a great little Friends of the Library group that may be able to get us some more computers."

What are the challenges in relying on volunteer support of this kind? How do you plan ahead in case that volunteer is no longer able to assist the library?