I am the same way SG. My ex and I would be driving along and I'd go "did you see that sign? _____ was misspelled." He was always amazed at how things jump out at me.
In staff meeting today I ran to get my reading glasses, came back to my seat, glanced down at the 4 paragraph paper in front of me, and realized my coworkers used "it's" as possessive. It was in the middle of all those other words but it's like it glared at me.
Another case in point. Anyone have a BP station nearby? Look at the sign listing for the "Ultimate" gas. the i and the m are together. I can't illustrate it here but just think of it as the dotted i is the first leg of the m. Who notices? No one. Well, me. I've never figured out why, but I wonder if I point it out to them I win some kind of contest or something.