Yep, I have some kind of intranet website that forces me to ask some questions I may forget :
Customer name/adress/tel/e-mail
Instrument brand/model/color/serial nb
Tuning/string gauge/playing style
List of things to do on the instrument
It makes invoices, quotes and worksheet based on these informations.
The program was made by me and a friend (in french). I owe him a 5 string bass for this work. Should I be considered as an horrible miser, I don't think I'm ready to give it to anyone, sorry.
Before having this program, I had a free software named "facturation v4" that is no more free now. It was a french software, so I doubt it would help you. Maybe you could find some native english free software that would let you use some custom fields to record specific fields? Try something like this if it can be of any help : http://sourceforge.net/search/?type_of_search=soft&words=invoice
It seems pretty easy to come up with your own, and I have sort of made one up, but I do not do the volume that may necessitate utilizing this document.
I pretty much just use a blank piece of paper. If photos are taken, maybe put them with it for future reference.
Work quantity is an important parameter, I agree! As long you do few repairs, a piece of paper (copy a form) is all you need. When you're a full time luthier and deal with dozens of guitar a month, it becomes interesting to use a software.