But might be a magic find item "restriction".
Means items max mf + valor = "mf cap"
Then the bonus is affected by exponential decay.
This means that the more MF you increase, the smaller the bonus is per point of MF.
Just discovered a quote;
"Bashiok: Well I don’t think it’s a linear scale, if that’s what you mean. We might share what it is on our game guide sometime after launch. "
This suggests that it is the same as magic-find on diablo 2, and is affected by exponential decay.