Every business plan should address the web, but not every business should have a web site.
You have a small local service business with a well-established customer base. You are very profitable. Maybe you’re an orthodontist, and you have a steady stream of clients from the local dentists. You really stand to gain very little from a website, or even an ad in the phone book. Simply focus on the services that have made you successful.
You sell stuff. Some good stuff, some not so good stuff. Sometimes, you have good months and you make alot of money, other times, you don’t. The web probably won’t help you stabilize the sales, but you may want to consider eBay or Amazon as a sales channel. Visit those sites and read the materials - they are excellent.
You have a strong mail order business, but your web sales are very poor. This is probably an indication that you should update the web
You’re passionate about something and want to share that passion with people, as well as let them participate. Create a social network - consider services like http://ning.com, or a Yahoo group, or other sites that allow you to create a community without any help.
You want to inform people about a particular topic, more as a resource than an opportunity for interaction. Try a blog - like https://www.blogger.com/ or any of the other free blogging services.