I proofread, write, and copy edit for clients. Because I spend so much time immersed in words, I am very aware of incorrect spelling and grammar.
I had to learn to read in a new way (and not subconsciously proofread) when I first tried Twitter. Creative spelling is a necessity when one has much to say and only 140 characters in which to say it. Now I truly appreciate both the amount of useful information that is shared and the succinct manner in which it is conveyed.
However, grammar and spelling are still important. Teachers desire correct, well-written answers. Employers want exceptional people whose words and deeds reflect positively on the company. Clients seek expert problem-solvers they can trust. All of these people may determine how right (or how right for them) you are within seconds based on how you express yourself. If you are unsure of your choice of words or correct spelling, check the better writing tips at AskOxford.