Does spell-checking software need a warning label? (Dennis F. Galletta, Alexandra Durcikova, Andrea Everard, and Brian M. Jones in Communications of the ACM, vol 48, no 7, July 2005). The answer is, "yes." I've known this for a long time, but then I've also made the errors this article talks about. Based on their survey of undergraduate and graduate students, people put much more confidence in grammar- and spell-checking software than they should. Their subtitle gives you the plot
Users---ironically, often those most verbally armed---put too much trust and little effort in questioning spell- and grammar-checking programs.
The researchers found people consistently trusted what that the language checks were correct and complete, when they are not. The redeeming quality of language-checking software is that it raises the bar for people who have difficulty with the language. Unfortunately, it also lowers the bar (somewhat) for people who are very good with the language.
I suspect most people don't realize these tools are fallible and rely on them out of the box. I use spell-check regularly and believe I know what I'm doing when I write. I also use grammar-check, though I am less confident in its recommendations, and treat them accordingly.
My favorite personal error was when I wrote something to my wife about "job opportunities at Searle" when I was out of town. The email spell-checker didn't recognize Searle, even though I worked for them, and I blindly accepted it's suggestion of "Seattle." The resulting sentence created some confusion at home.