A response from a human that says "I hear you, and I'm going to think about this and get back to you" is perfectly valid. It ensures they don't feel ignored, but buys you time.
On feature requests, resist the temptation to do everything everyone asks for. Most feature requests are one-off, idiosyncratic stuff you don't need to do.
Instead, ask yourself (or the customer!) why is the customer asking for this? Rather than the mechanics of the feature, ask what problem the customer is trying to solve. Ask what the customer is trying to accomplish. Often the correct feature accomplishes the root goal but not exactly in the way the customer suggests.
Take a breath, don't worry. You have people who love your stuff -- they won't abandon just because you don't do their pet feature request tomorrow. Think about the iPhone -- how long did it take to get copy/paste? It's hard to chill out -- I know! -- but you can.
Customers who can't wait for their feature to be implemented.... you don't need them and their stress!