Spell Check and AutoCorrect can be wonderful tools. They have all but eliminated one of my great pet peeves of all time, namely the misspelling of the word "deity" (meaning a god or godlike being) as "diety." Some of my favorite writers used to make this mistake, and every bloody time it had the effect of completely knocking me out of the story narrative. Thanks to modern software, though, this has all but gone away completely.
What has gotten much worse, though, is the misuse of homonyms. Spell Check is not Usage Check, at least not yet, so words that sound the same -- their, they're and there, for example -- are often used interchangeably. And incorrectly.
So for the record, here are a few of the worst -- now go ye, and sin no more:
HOARD -- a dragon's stash of gold and goodies
HORDE -- a huge group of something, like Attila's Huns, or lemmings headed for a cliff.