If you have used Google Docs, you can see the potential for businesses. If you haven't tried it and used it to share documents with others yet, do so.
The ability to share documents--for viewing or for collaborative work--is one that has enormous implications for worker productivity. Every business ought to at least evaluate this and see what it is like. It costs nothing to get into it, and the savings in cost and improvement to productivity should speak for itself.
If a company has fewer than 50 employees who need access to email, etc., then it can sign up for Google Apps for free. Google Apps includes email, calendar, and Google Docs. If there are more than 50 users, then the company can use Google Apps Premium, which costs $50 per user per year. For email alone that is a bargain compared to alternative email hosting in-house. You can then consider the calendar and docs as freebies on top of that service, adding extra value to the service at no extra cost.
The true cost savings that comes from using Google Apps in businesses is often not calculable, because so few companies accurately count the cost of administration work, electricity for servers, increased air conditioning to keep servers from overheating, etc. Amazingly, businesses often don't count the costs of the servers and storage themselves, or the bandwidth used to process email, filter spam, and make backups.
All these hidden costs mostly disappear with Google Apps.