I tried searching around but it's surprising how muddled the information on skill books is. I've been leveling all of my skills without ever reading a skill book. I planned on saving the skill books up until I get a few of the tougher skills *cough* enchanting *cough* up to 45 or so before I begin to read them.
Does it actually work that way? A lot of people seem - or seemed, at least - to believe that skill books only worked for certain skill levels.