I like this bit: "It also looks at articles that contain flags like (sp?), which is the author telling us that he or she failed high school English."
The poor spelling found on the Internet creates a positive feedback loop that makes it increasingly difficult to spell words properly.
Before wide acceptance of the Web, most written words appeared in magazines, books, newspapers, and other sources which were, hopefully, reviewed by professionals with more knowledge of spelling than the average person. If you were unsure of a spelling you could write out the word and easily recognize if the word matched the ordering of letters that you had seen so many times before.
Now, for some words, you've probably seen the improper spelling more often than the correct spelling. That makes it more difficult to recall or recognize the proper spelling. For children subjected to this misspelling onslaught at an early age, it must be worse. I suppose many of these spelling problems would not even exist if English were a more intuitive written language. However, I expect this all to go away as grammar checkers are embedded into web browsers.