One of my biggest problems is that I often type form instead of from and because it's close I usually don't catch it, and since it's a real word spell check won't catch it either. This is why, with important documents, it's good to have several people check it very carefully. And sometimes even that doesn't work.
In Michigan, they are having to redo the ballots after is was discovered that in a ballot initiative the word public was spelled without the "l". Hee.