This sort of approach is a classic way of doing cheap usability testing. If you've not done this sort of work before I'd recommend getting hold of the (short a

This sort of approach is a classic way of doing cheap usability testing. If you've not done this sort of work before I'd recommend getting hold of the (short and entertaining) "Rocket Surgery Made Easy: The Do-it-yourself Guide to Finding and Fixing Usability Problems" by Steve Krug. It'll give you a bunch of useful tips on how to get the best out of our time.