Plus you get a bunch of free work out of every applicant if you delegate real issues out as work-sample tests :P I'm pretty sure the new Audi A8 cup holders are from my mechanical design engineer third round volkswagen interview a couple years ago
It's nearly impossible to scope useful, shippable work that can be accomplished in a job interview. Otherwise, you're asking for 20+ hours of work, which means that only fools / suckers will do your interview.
Do you really want a company full of fools and suckers?
Shippable, goodness no, but a 1-hour-limit prototype already solving a problem you haven't even begun thinking about? I'd take that. I tend to start over from scratch after the first prototype anyway. You're interviewing people anyway, your choice is either real issues or fake issues, and fake issues get your nothing.
