Are the Brewers going to regret trading Brett Lawrie for Shaun Marcum?

Not at all. With Shaun Marcum they are tied for 1st in the NL Central. They already have a very strong offensive with Fielder, Braun, Weeks etc... so if they loose then it definitely wouldn't be Marcum's fault. They really needed a good pitching staff and Marcum was perfect for them.