I spent a little more than a year as a copyeditor/proofer (at a company where a missed typo could potentially sink the company). I learned to read letter by letter and became paranoid that every word is misspelled or misused and that most of the puntuation is incorrect. It's pretty well changed how I read; I catch typos in books even by major publishers. Every once in a while I'll get really lucky and find a paragraph alignment error or a missing header.

It can be a little distracting, but that would be my recommendation -- proof a text like your job depends on it, reading character by character and/or look at the typography and page design for inconsistencies.