Writing is always far more about the story than the spelling; Kiya is right <img src="/ubbthreads/images/graemlins/smile.gif" alt="" /> Edit: As long as your story is still readable/comprehensible!
It can be a real problem if the sense is lost though - as in 'Rogue/Rouge and 'A Lot/Allot' etc - where the actual meaning expressed is quite different to the intent. Most of us tend to be far more indulgent of writers who are writing in a second or third language too, for obvious reasons.
Someone whose first (And often only) language is English should certainly not be making such elementary mistakes.
Further, some characters who are narrating their own adventures will think as they speak, which means using odd words or "droppin' the reggallar spellin'" just to make the point that this is the way the character themselves thinks.
"This is MY style" is not a good reason for poor English in a native writer - "This is the CHARACTER's style" is always a good reason, especially if you are writing in first person perspective.
As for 'Organise/Organize', 'Colour/Color', 'Defence/Defense' and other words that seem to have multiple correct forms - blame the Americans! <img src="/ubbthreads/images/graemlins/biggrin.gif" alt="" /> Seriously, English and American English have several notable spelling differences, and as most of us will see both forms of spelling it can get very confusing as to which should be used. As a general rule, the more phonetically correct version will be the American spelling - but for the Web, either will really do <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />
Hope this helps clear up any confusion <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />