That "into/in to" one: there are quite a few of those that confuse the semiliterate or the careless non-proofreaders. All together, altogether. For ever, forever. May be, maybe. Any way, anyway. And the worst of the lot, All right, alright. Stuff like that. For decades we had a telly programme called It'll Be Alright On The Night. Grr. Apropos of "into," we were told by our priests at school that "onto" is not a word and we should never write it (they also told us to never end a sentence with a preposition or to start one with "And" or "But"). They were just dead wrong, of course. I mean, "onto" has been an English word since at least 1518...

One thing that crops up a lot and which peeves me every time is "and therefore...". Pig ignorant!