With 4 years experience with the same offense, Chris Redman was beaten out by a rookie that held out the first week of training camp.
In the short term, I see no difference in starting Boller over Redman. Whatever number of games Boller will lose making the unavoidable "rookie QB" mistakes, he'll conceivably win other games making plays that the slow, noodle armed Redman couldnt make.
In the long term, the sooner he gets through the growing pains of learning to be an NFL QB the better for the Ravens.