Dana Eveland is injured and is out at least a month. I had an interesting e-mail conversation with a Brewers fan a couple of days ago about Vargas's future with the club, which led to the details of the MIL-ARI trade. Like the Carlos Lee deal, it's a lot easier to evaluate it if we can agree on who was traded for who, exactly.
I've assumed that the deal was Estrada-for-Davis and Eveland-for-Vargas. In the first case, each team traded from depth to fill a hole; in the second, the Brewers traded higher upside for more guaranteed major league readiness and innings chewing. Eveland is still only 23 (he turns 24 in the offseason), but at the same time he has yet to show much of anything in the majors. He's had another good year in the minors (2.70 ERA with tons of groundballs this seasons), but suffered just as much in his two MLB outings this year as he did in his stint in Milwaukee last year.
There's still plenty of time for him to turn it around, but I suspect that the D-Backs aren't counting on it: they're simply piling up as many arms as they can in the hope than one or two of them pan out. That may turn out great for them, but either way, it's easy to see this trade becoming a clear win for the Crew.