It all depends. Generally I dont like to go over 150 either. BUT.... if the situation represents itself where I think a -165 line should be -195 or something like that I will play the game. Try to stay away from laying that much juice though.
I played Arizona the other day with Webb on the mound against Zito at -160, I felt the line should have been more like -200. That said, I don't do that often at all.