Part of the fun when it comes to optimizing a site for search engines is guessing how people will be searching for your site. This means that most SEO types spend some time asking, "What are keyword typos that people may try?" After all, if the typos are common enough and allowed for then it makes the site easier to find. In a lot of ways it is knowing that "pwned" is used in place of "owned"; putting one word or another may drive visitors to the site, but putting both in will really increase visitors.
A good source of typos is to look at grammar sites, especially those that take close looks at common typographical errors and list them, as well as what people were really trying to type. There are other sites that look at why those typos occur, and list the common errors, or even patterns of errors. Hanging out on grammar discussion boards can also give you some good ideas.
By taking advantages of these kinds of sites, and placing purposely made errors along with the correct forms in the meta-data fields, you can make your site even better optimized, and obtain more visitors than you had before. Taking advantage of other's errors is usually seen as a weak way to go, but in this case it is just part of the job.