i'm so glad this thread started. i noticed this right when i activated the phone. i came from a galaxy nexus but owned a iPod touch and i could have sworn i was much better at typing on the iTouch then what I am experiencing on the iPhone 5. i wonder if its the new screen or something they tried different with the OS. regardless, i am definitely making more mistakes than i did with the iTouch.
my biggest problems on the keyboard are hitting the letters close to the edge of the screen, like P, A, etc. i also seem to hit the backspace a lot when i reach for L or M. as someone else mentioned, when i type fast it seems to skip letters. hope this can be improved with future software upgrades!