Spelling words incorrectly has been a trick used by marketing gurus for years. With the advent of the google built in spell checker this practice has slowly been diminishing in effectiveness. Certain words, however, are spelled incorrectly by the public: Cell Phones or Cellphones? And then there are different languages such as british english: Color or Colour? By writing articles which associate themselves with the less common spelling you essentially are creating a niche with a topic which could be very difficult to enter in under normal circumstances.
The weight loss niche is a very difficult area to get in the top 10 on a google results page. However, by spelling the word weight as weigth I managed to get #2 on google with one of my key phrases in the weight loss category. This of course was dependent on the user typing the word weight incorrectly.
If you are trying to figure out the best way to mispell a word, aim for letters which are on opposite sides of the keyboard. This way the user has a better chance of hitting the wrong sequence of keys because they need to coordinate both hands at once and this is why many people will accidentally reverse letters that fall opposite of each other on the keyboard. Probably the most mispelled word in the english language online is "teh." See how the t is on the left hand, h is on the right and e is on the left again?
Another neat trick is reversing keys on the keyboard. For instance, you could type k instead of d in a word. Your goal here is obviously to catch someone not paying attention and lazily typing in the word.