I'm starting to do some job hunting for a professional programming position and I'm a bit nervous about these types of interviews. I think I have the skills, but having been a solo programmer for a long time, I'm nervous about people looking over my shoulder and watching while I try to think through a problem. It's probably more a lack of experience with these types of interviews than anything else.

As someone hiring a developer, can't the submission of previously written code provide good insight into the type of person you're interviewing, or is there concern that the code is not really theirs?