Yea, I think McBadgere said something about before 1.5, he (or one of his kids) could spam hundreds of iron daggars, and level up quicker than they could after 1.5 doing the same thing. The item has to be of a higher value (I think) for you to level up faster.
SubRosa, it must be due to the tome. Gotta be. All of my characters have found it so far, but none of them have used it. Gunter doesn't use magic, for instance, and probably sold that tome for gold. His Smithing levels up so slow...I always make extra items that he sells (rather than wears) and it still levels up slowly. He's not even able to manufacture Orcish pieces, yet he's Level 17 or 18!
Gunter could try harder though. He could take up mining, for instance.