Grammar and spelling are important...

"I've survived just fine without bothering about grammar."

Are you quite sure about that?

Have you, perhaps, wondered why you didn't get the job that you felt you were so well suited for? Or why nobody bothers to reply to messages you post on internet bulletin boards? Or why you didn't get many responses to your personal ad?

Job applications: Many employers are immediately put off when they receive a poorly written cover letter with a job application. Many will simply toss them into the big circular filing cabinet on the floor without even looking at the rest of the application.

Messages: I subscribe to a few technical mailing lists, and try to help people with their problems when I am able to. But if I have a hard time understanding what the person is trying to say, I leave it and move on. I don't have time to try and decode their badly-written comments. I know I'm not the only who does this: poorly-written messages consistently receive fewer responses than well-written ones. I do make an exception for people whose native language isn't English of course - although the sad truth is that people who have learned English as a foreign language frequently have a much better grasp of English grammar than those whose native language is English.

Personal ads: I've heard a comment like this several times when discussing online dating: "The first thing I notice is how the profile is written. If it's badly written I move right on to the next candidate."