Re-roll take worst?

[MaxMahem]

What is everyones opinions on giving a character a "re-roll take worse roll" penalty in d20? If I understand the statistics correctly, this should give a player the largest penalty (~25% or -5) on average checks, those they need to roll a 10 to succeed on. While the penalties on checks they are either very likely to succeeded on or very unlikely to succeeded on is proportionally less. (The penalty is equal to y=(x^2/400)-(x/20) where x is the number they need to roll and y is the the percentage penalty vrs a normal roll).

It seems to me that this would be a creative option for bestow curse or an interesting way to display a characters ineptitude with something, such as color-blindness or a natural clumsiness. Thoughts?

[Umarth]

I like the idea of using it for bestow curse.

For something that's going to be a perminant effect though you're probably better off going with a flat modifier to reduce the number of rolls required.