He's headed to the Brewers in exchange for outfielder Chris Dickerson. In 2009, Dickerson had the looks of a decent third outfielder/strong 4th, but he hit only .206/.250/.268 in 2010, in the process being traded from the Reds to the Brewers. ScoobySnacks points out that he broke his hand last season (confirmation).
The Yankees are obviously hoping Dickerson can return to his .275/.370/.373 2009 level. I'm surprised Greg Golson didn't get a shot for the first week or two while Curtis Granderson is nursing his strained oblique back to health, but the brass must have felt that Golson's own oblique injury must have set him back too far to be ready for opening day. Dickerson has played all three outfield spots, so he's probably the backup center-fielder for the time being.
Well, Sergio, I wish I could say I hardly knew you, but I saw you serve up too many gopher balls in the last couple seasons. I think you were a useful spare part, but with Colon, Garcia and Nova all looking good, you're just a redundancy.