I\'ve said it before, and I\'ll say it again:
Any skill system that discourages players from creating \"interesting\" players by forcing them to loose experience in their skills seems like a terrible idea.
I see what you\'re getting at, trying to keep things balanced. However, this will occur naturally in the game: a person who spends half their time learning swordfighting and half their time learning magic will be able to perform both skills with relative effecitiveness. However, he will never be as good with magic as a pure wizard, or as good at fighting as a true swordsman.