Here's the Boston Globe's Bosox blogger on the trade:

A few Mo' questions

The moral? Don’t make any “gentleman’s agreements” with the Red Sox.

Scratch off another member of the ever-disappearing 2004 World Champs today, as the Red Sox sent Bronson Arroyo to the Cincinnati Reds for outfielder Wily Mo Pena, a 24-year-old slugger who hit 19 home runs in 99 games last season.

Arroyo, who won 14 games for Boston in 2005, had his first decent outing since arriving in Florida this month yesterday against the Orioles. He signed a hometown-discounted three-year, $11.25 million contract in January with a handshake from Theo Epstein that indicated the team didn’t have plans to trade him at the time. It was a deal he went against the advice of his agent to sign.

Oops.

Now, besides what this does for Avalon’s off nights in the summer, one has to wonder what it means for Trot Nixon’s future in Boston. The right-handed hitting Pena will likely platoon with Nixon; but at 24, the much-younger Pena is certainly more in the long-range plans for the franchise than a guy like the oft-injured Nixon, who at 31 is signed through the end of this season. But with the continued offensive struggles of third baseman Mike Lowell, there remains the possibility that Pena could see time at first base, allowing Kevin Youkilis to return to his more natural position across the diamond.

That is, of course, as long as Pena matures as a hitter. Right now, he’s nothing more than Dave Kingman or Pete Incaviglia. Is he worth trading a young and versatile starting pitcher that was willing to go to the bullpen for? That can be argued, and likely will be for this entire season.

Again, as the Red Sox have handled themselves all winter, this was a deal with an eye on the long term, not a six-month sprint to October. Arroyo is just 29, and while not a blue chip prospect, was a 14-game winner last season. Now, it can be argued fervently that Arroyo topped out in 2005, that to expect him to match or better than performance is unrealistic, in which case the Red Sox would be crazy not to get value for him while his value was still high. After Arroyo struggled all spring, Epstein probably could only wriggle out a decent deal after yesterday’s performance against Baltimore and struck while the proverbial iron had some heat to it.

But Pena is a weird choice for this lineup, one predicated on patience at the plate, of which Pena has none. He has a pathetic .303 career on-base percentage, but is coming off a solid performance for the Dominican Republic in the World Baseball Classic, batting .400 over three games with one run driven in. He also might conjure unpleasant memories of Mark Bellhorn, who struck out 116 times in 311 at-bats. That’ll go over well with the crowd.

How much of his prior performance is based on youth and immaturity? Andruw Jones took almost an entire decade to mature into the All-Star player he is today. Despite a waiting room full of hope and hype, it never happened for Jose Cruz Jr. Where Wily Mo Pena lies among them remains to be seen.