Wonderful question! ++

Your point number 3 is very important, as in what context is the misspelling occurring? Also, defining what a mis spelling is is important. e.g. For people through to many things four there friends too catch. vs. fuor pepole trhew too many things fro thier friends to catch. Another catch may be misspelled words such as "Suzeez Donut Shoppe"

If you are looking for a way to sample spellings that you may have some control over, write a spider program to grab web pages, then spell check those pages. Presuming of course the pages you scan are written or proofed by the types of people you wish to test. Count misspellings.

Great fun dageek