I really don't like the idea of trading any of our (Crespo designated) "Big Three" of Sanchez, Lester, Papelbon. That being said, I think Burnett's inconsistancy can be justified a little. '02 was his first full time starter year and he went through some growing pains while showing flashes of brilliance. '03 and '04 were shorted and disappointing due to real pains as he was injured. '05 is really his second full time healthy year and he is definitely improving. With his stuff the ceiling is still very high for him. Health is always a concern. He's at least made it to the show and performed, something that an injury could prevent any of those B3 from ever doing.
EDIT: Arroyo still has some ceiling room too. With the quality of his offspeed pitches, he has the potential to be a solid middle of the rotation starter. But right now, the book is out on him. He's having a lot of difficulty locating his FB, which max's in the very low 90's. That velocity will work in the bigs if you can locate it, but Bronson hasn't achieved full command of it yet. As long as his location is struggling, hitters are going to sit on the curve in the zone and hammer it.