Almost every church in America now has a web site. Many I have seen would be better served if they did not because having a poor to average web site is worse than having none at all.
They are very important in reaching new people because they will probably visit your site before they visit your campus. If they are disappointed with the site because it was done poorly or if there is obvious outdated information they will probably not come at all.
The two most important things about web sites are that today they must go beyond words and pictures. People want to experience your ministries before they buy the live product.
You must provide quality video and audio capabilities so that people can see and hear your worship before they come. They want to know what type of environment their children will be in and something about the quality of programming they will be offered.
The second most important thing about a web site is that it will never take the place of a relational connection that your people are making with unbelievers during the week. The web site is an important step but it will always be the second step and in and of itself it will not automatically draw people to your church.