I can't help feeling sorry for Lewes MP Norman Baker, who spelt Sussex as "Susex" on the front cover of a booklet sent out to constituents.
I'd class this as a typo rather than a spelling mistake, as I am quite sure Mr Baker knows how to spell the county he works in.
Everyone makes mistakes like this and it just highlights the fact that when you are writing, you need to take a break before giving your work a final read. Have a cup of coffee, write an email or make a phone call and then come back to your document with fresh eyes.
If you do this, you will find it much easier to read what is actually on the screen rather than what your brain thinks is on the screen.
Another trick is to print the document out - you will find it much easier to pick up mistakes on paper. Even better, get someone else to read it over for you.
And don't forget the spell check, though the final read through should always be done by a human rather than a computer.