I’m in iPhone-analysis mode, will get this out of my system! Since the introduction of the spellchecker, I’ve experienced a significant drop in speed and accuracy of typing.
My spelling is usually pretty good, and the initial iPhone models’ input processing was focused on fixing “fat fingers”, i.e. the wrong key pressed, and it felt a little bit like magic. I’d just type away and I’d get what I meant appearing on the screen.
But with the spell checker, my input gets changed to words that aren’t near what I mean, usually because my incorrect input is closer to another poorly-spelled word than to the poorly-keyed word I meant. Perhaps they’ve identified that the majority of users would be better served — but it definitely degraded the experience for me. Switching spellcheck off has helped, but it kind of goes against their interface principle of getting the defaults right.