One of the worst things, in my opinion, is how modern autocorrect fixes words that I’ve misspelled into correctly spelled but inappropriate words. What’s worse is the way Mac OS X arrogantly assumes that I must mean the word that makes no sense in context, because it is closest to the typo I just made.
For me, it’s far better to just see the red line of doom; that way< i can right click and choose the right word, or just type it again. I mean, it's typing; it shouldn't be that big a deal to do it twice. If you're like me and want to turn this "feature" off, here's how.