At this point in 2009, the Brewers were stuck in a tough spot. Rickie Weeks had been out for over two months (and would miss the rest of the season) with a wrist injury, and the Brewers had been splitting time at second base between Craig Counsell and Casey McGehee in his absence. Counsell was having an excellent season and McGehee was in the middle of his burst onto the scene, but neither was really suited for an every day job at the position.
The Brewers responded by acquiring Felipe Lopez from the Diamondbacks for two minor leaguers: outfielder Cole Gillespie and pitcher Roque Mercedes. Lopez would go on to make Doug Melvin look like a genius by having the best few months of his career: In 66 games as a Brewer he hit .320/.407/.448, compared to .265/.334/.393 for his career. In two-plus months as a Brewer he was worth 2.6 rWAR. He was never worth more than 2.5 in any other major league season.
Meanwhile, the players the Brewers traded away in the deal haven't done much. Gillespie turned 27 a few weeks ago and has still played just 45 major league games. He's spending the 2011 season on his third tour of duty in AAA. Mercedes is back in the Brewer organization, having been claimed off waivers from the Diamondbacks this spring.