People with horrid spelling, who obviously SPEAK the English language well enough, but can't be assed to learn how to write (or similarly, and especially, those who write in forums like it were a multiplayer chatline during a huge firefight, or God forbid, a CELLPHONE) piss me off beyond all reason.
I made a personal vow to never be like them, so I proofread everything live for spelling mistakes (if I notice a word gone wrong, I wont wait to fix it), then reread for grammatical errors.
For Heaven's SAKE kiddies! You have MUCH more than a fraction of a second to type, on a full-sized QWERTY keyboard, you have time to print a couple extra letters.
Summary: "U" IS NOT A WORD! TYPE IT OUT!