For a chat room or mailing list, the answer is probably no. This fact, however, is not an excuse to avoid the task of proofreading web pages. The fact that we live in a global environment is all the more reason to check for spelling and grammar. Because your web page has the potential to be viewed by anyone in the world, mistakes also have the potential to be viewed by the world. While the web is quickly becoming a selling tool, the web is still primarily an information tool.
Pictures are abundant, but the written language is still the primary communication.
Incorrect grammar or spelling could lead to misunderstandings or incorrect information. The real world needs real words. As a visitor or a customer at a web site, I lose confidence in the site's services when a spelling or grammar mistake glares at me from the first page. As more and more services are provided via the web, consumer confidence becomes more important. Spelling and grammar mistakes diminish this confidence.