The last time the Los Angeles Angels of Anaheim (of California) traded the St. Louis Cardinals a center fielder for a pitcher things didn't turn out so great. Peter Bourjos is somewhat less likely than Jim Edmonds was to turn into Ken Griffey, Jr., Jr., admittedly, but the news that the Angels are interested in Marc Rzepczynski--and willing to trade Bourjos for a reliever--is at least a little redolent of the Edmonds trade from 12 years ago.
Bourjos would be an interesting get for the Cardinals. Right now we know this about the 25-year-old: He's right-handed, which would go well with Jon Jay, and he's one of the two or three best center fielders in baseball, on defense. On offense--well, it's anybody's guess. He was average-to-above-average in the minor leagues, then really solid in 2011, and now really terrible in 2012.
In short: The kind of resume that gets you traded for a left-handed reliever. I'd make the trade, if I were the Cardinals, but only if I had no plans to ever return Rzepczynski to the rotation, where he was actually very solid during his career with the Blue Jays. Bourjos offers depth in center and the possibility of more than that; at his best, Rzepczynski is never going to be anything more than a left-handed reliever here.