They have been significant, but not to the point where he's been bad on the road. He's had about a .350 OBP and .480 SLG on the road in 2005/2006. OPS+ adjusts for park factors, and he's been pretty good, outside of 2003, in that department. Nothing special, but pretty good. Think Carlos Lee territory, but younger, and much fewer years committed on the contract. (edit, while his baseball age is younger, he's actually only 4 months younger) Plus, in Cubs thinking, he's killed in Wrigley. :P (no, I don't put much stock in that claim).