I don't think there's anything necessarily wrong with this technique as long as a company makes it easy to contact them some other way. If you have a reply-to address that actually accepts mail, then any large mailing (which isn't always a bad thing) is going to receive a massive amount of vacation auto-responses, chain letters and the like. It isn't exactly the most friendly gesture but it's for very practical reasons, IMO. I wouldn't judge a company's customer service on this alone.