Milwaukee received former All-Star catcher Johnny Estrada, right-handed starter Claudio Vargas and right-handed reliever Greg Aquino for steady left-handed starter Doug Davis and a pair of prospects, lefty Dana Eveland and outfielder David Krynzel.

Estrada's become a hacker but can hit for some power.  The purpose of the trade is clear in this quote:

Estrada was acquired by the Diamondbacks in a trade with Atlanta a year ago. Despite his success at the plate, Estrada was unhappy in Arizona and made it clear late in the season he would prefer to move on.

Davis has a serious walk problem (he hit triple digit BB's last season, averaging around 4 BB/9) to go with his K prowess, but even with that, he's an improvement over what was dropped.  Vargas is just trash who might be mediocre in his prime, and Aquino has a gopher problem, making him mop-up fodder at best (30-35 IP each of the least three seasons because of this).  And then of course, getting prospects never hurts, so bully for the D-Backs.  I'd have to say I wonder what the hell the Brewers were thinking.  Sure, you just got yourself a good hitting catcher, but at what cost?

Pitching wise, this is a huge upgrade for the D-Back staff, which already has Brandon Webb and Livan Livan Likes His Innings, and got a couple of prospects to boot.  They managed to unload a disgruntled regular and net a great return.