I make it a policy never to act on a customer request without making sure I understand why they want it. What problem are they trying to solve? What value do they expect to derive from this change or addition (or subtraction)?
Sometimes you find, if you understand the few underlying problems, you can come up with a single solution that solves the needs of many customers at once. This can shrink your customer request list down to nothing in short order. It is a powerful technique, but getting to the root "why" is sometimes harder than it sounds.
How to ask why? I have a few tips. Read this piece I wrote for the Boston Product Management Association's blog for in-depth discussion. What are your tips for getting to "why?" Write back.
My friend Charlie Baker at Oracle/Dyn is looking for a product unicorn. He needs someone with the skills of a product manager and a background in web application firewalls and distributed denial of service attacks. Let me know if you or someone you know is in the zone and I'll try to hook you up.