Last year, the Tigers got Sheffield really fast, and this year, they plug the new hole at SS with Renteria. Carlos Guillen moves over to first, which is a big upgrade on Sean Casey, and Renteria, also an upgrade on Casey, moves in at shortstop.
The Braves get RHP Jair Jurrens and OF Gorkys Hernandez in return for the 32-year old shortstop.
Renteria has generally been an overrated player his entire career, but his 2007 was his best offensive year since 2003, which was his other really good season. His rate stats were essentially the same as that season, but his speed has dried up, and his fielding has become a real hassle.
Honestly, I don't much like the trade for Detroit, but if the Tigers are fortunate, Renteria will hit .290 or so with a bunch of doubles and provide a stable offensive presence for a year or two.