Three times this week alone I have emailed companies that are vying for my business and they don't take the time to respond. Why would I do business with them? I get that you might be busy but it takes just 15 seconds to respond with "Thanks, we got your email. We are a little behind but I should be able to get back to you by ___."
A simple gesture like this lets me, the customer, know my message has been received and it will be attended to at some point. Even if you have to do an auto-response email (which I hate) at least I know you got the email.
Study after study has shown that the faster a business responds to inquiries, the more likely they are to get the business. If you can't take the time to respond to people who are seeking out your business, then don't complain when things are slow. In fact, take the contact information off your website because if you can't handle the logic of basic communication you probably don't deserve to be in business.
Another thing. If you send out an email newsletter and do not make it easy for a subscriber to respond to you, unsubscribe, or find your contact form on your site, you fail. (And chances are good that you are violating the FTC's Can Spam rules.)
Remember The Golden Rule? (Do unto others...) Do this in business. Picture how you want to be treated as a customer and do this for your own customers.