Great, shabbir. You have addressed your mind on a matter many don't take seriously. As all know, poor grammar and poor spelling makes the reader feel a headache when reading. In many websites, I have felt such headache. I think, when you write, you must try to make it look professional.
As you have said, upper case and lower case spelling is extremely important. Use it correctly. And never forget to spell check your final product. Really, your composition is a reflection of your personality. And nobody will want to project a poor personality of himself.