First of all, why would you be interested in misspeling?

• 1. To avoid getting your pages hit by a duplicate filter if you are using “borrowed” content or scraped search results. You might also increase your traffic by ranking for misspellings/typos. There should be millions of search queries that are misspelled each month.
• 2. To increase the variance in a pseudorandom text generator.
• 3. For e-mail (and newsgroup) spam so spam filters don’t hit you so much.
• 4. To avoid any other kinds of message filters.

Here is some sample code for an automated misspeller.

The above takes every word of your text and switched the places of two adjacent letters.
If you want to make your own and take the above as an example here are some extra tips:

a. Don’t misspell every word. Make it so you can customize the percentage. You need a small percentage of misspelling if you plan to do this on sites, otherwise your pages will probably suck.

b. If you don’t want it to fuck up your keywords, you can make it misspell your text before your keywords are insterted or make an option to add a list of keywords/phrases that will not be changed.

c. Add some common types of typos to be replaced, that are not just two letters switched. For example the suffix -ing can be replaced by -in or -in’ or -ig or -ng.