While Pena has "potential", I'm concerned about his frequent strikeouts and average-at-best fielding ability (plus I remember laughing when Yankee fans would pump him up when he was in their farm system).
But knowing that Nixon will go on the DL at some point this year, and that Arroyo is pretty much a league average pitcher (ERA+ of 121 and 98 in his two full years here and he's what, our 5th or 6th starter?), I can't find much of a downside to this deal. If Pena gets playing time and can bop 30-40 or so home runs, this will be a steal.
Some Theo comments from a spot on WEEI (thanks to SoxScout at SoSH):
This guy has the potential to be middle of the lineup player. ... The track record of players this young and this powerful is very good. ... Tools are so good and development has been so hindered that he isn't even close to tapping his potential. ... We accept the fact that the strikeouts are going to come, fans need to also, but his power will make up for it. ... We are going to get him as much playing time as possible. ... This is a great situation for him with Ortiz, Ortiz spoke highly of him.SoSHer (and Reds fan) "osuceltic":
Great raw talent. He's an absolute physical specimen. Huge and ripped. Huge hands. Good speed. Strong arm. He has off-the-charts tools. Unreal power -- when he hits them, they stay hit. ... Has worked hard to improve himself. Had one of those contracts that guaranteed him a big-league spot too early, so he really didn't get the minor league polish he needed. ...Epstein also maintained there was "no-trade handshake" with Arroyo.
On the negative side ... Zero plate discipline. Awful defensive outfielder, although he obviously has the tools to improve this. No "baseball sense" either in the field or on the basepaths. Injury prone ... VERY streaky. He'll go through stretches where it looks like he'll hit any pitch out of the park, and stretches where he looks like he couldn't hit the ball with a sheet of plywood. ...
I really think he needs to play every day and I'm not sure he's ready to do that in an environment like Boston (tough fans, tough city, tough division, tough outfield). He really does play like a young Sosa, but will he ever develop his tremendous potential?