This is why I rarely mess with rookies, there's just no history to know what they'll do long term. WIllingham raked the minors, but that doesn't mean all that much, because in the majors, the pitching is so much better, and once they find your weakness, they'll pounce on that. obviously, it took the league a while to figure out what pitch either to throw or not to throw... To what degree Willingham can adjust is a big unknown. Some guys never do, some do a bit, some do great, and some become stars, but it's hard to predict and can take years.... That's why I stick with vets mostly. Vets have a track record and odds are, if they're cold, they'll heat back up soon.
I did grab Jared Weaver though after his first start. From what I saw in his first start, he's got stuff that you can only adjust to so much.