Conclusive proof that spelling matters arrives in the form of an analysis done by Charles Dunscombe and highlighted by the BBC. He says that spelling mistakes cost companies business on the net. For instance, the specific impact on one company was that sales doubled after a spelling mistake on the sales page was corrected. If it has such an effect on internet sales, we can extrapolate the effect on job applications, for instance, or reports.
I am forever telling my students to check their spelling. I don't expect people to actually be able to spell nowadays (more's the pity) but I do expect them to take a tiny (I emphasise the word "tiny") amount of trouble to use their spell check and to take a little more trouble to get used to things like apostrophes - check whether they're using "it's" meaning "it is" or "its" meaning "of it". I even give them a very limited set of handy hints (behind the OU firewall). I am usually talking to a brick wall - I make the same corrections at the end of a course as I do at the beginning. I need different strategies.
I am thinking of rules:
1) If I find mistakes a spell check would have picked up, you will lose marks
2) If I tell you a rule, like how to distinguish "it's" and "its", you will lose more marks.
But basically the skills for students are simple:
a) if it doesn't matter to you, make it matter, because it does
b) use the spell check before submitting the assignment
c) make a note of mistakes you make regularly and keep it pinned by your monitor
d) get to know my wiki, or another site like the University of Bristol's Improve Your Writing and make continuous use of it.
Meanwhile I can link to another story here, the one about the Swiss political party that has been set up with only one policy objective, to ban PowerPoint. Read the article here, and check the first line of the story.*
*If you don't see it, check the spelling of "soul".