According to a survey done of 460 Australian organisations with over a hundred employees, 59% don't reply within 1 week.

Granted, this survey has been done by a company who specialise in responding to your companies incoming email so it's likely to be a little biased - but my personal experiences certainly reflect their findings.

There is nothing worse than e-mailing a company (either directly or via their website) and not receiving a response. Being an internet-minded person I expect a response within a day or two, which I don't think is overly unreasonable - if they do not wish to respond to e-mails, they should not list an e-mail address on their website.

This is an area that small business seems to excel at - when there's only one or two people at the helm they pride themselves on answering customer queries in a quick and useful manner. Unfortunately the same can't be said for larger companies.