Recently the Pirates traded a young relief pitcher, Jesse Chavez, to the Tampa Bay Rays for 2nd baseman Akinori Iwamura. I've seen a lot of overreactions so far on this move; frankly there is not much to get excited about either way. There were some pros and cons to the trade that came close to balancing themselves out, as I'll explain.
Akinori Iwamura is a very average player, perhaps slightly above-average at best. That's not a bad thing; average players have significant value in Major League Baseball and even good teams have use for average players. Indeed the Pirates currently have few players that can even claim to be average. Iwamura for his brief 3-year career (he had previously played in Japan) has gotten on base at an above-average clip of .354 while slugging a little below-average at .393. In all he has a wOBA of .331 for his career, practically the definition of average. Both 2nd and 3rd base are tougher defensive positions, and he plays pretty average defense according to UZR (+1.5 for his career). He's produced 6.3 wins above replacement (WAR) for his career, or about 2.75 per 150 games played. Given that he's now 30 and had some injury problems last year, we might expect a bit of a decline but not too much. However, keep in mind that he put up those numbers in the better league (and the AL East at that), so he faced tougher competition than the Pirates face on average.
Major League teams pay very handsomely for each marginal win on the open market. Whether they realize it or not, in recent years they've paid about $4.5 million per WAR. By that standard, Iwamura could produce about half of his career average and still justify his contract. In that sense Iwamura is a great acquisition. Furthermore, he doesn't appear to be blocking any younger players (Delwyn Young was not that good in 2009 nor is he that young). Though there might be some, there aren't likely to be many players available in free agency that could add 2+ wins to the 2010 Pirates for Iwamura's salary or less.
However, the $4.5 million per WAR is a bit simplistic. Not all wins are created equally. There is a "sweet spot" somewhere near 90 wins where each additional win drastically increases a team's chances to make the playoffs. Teams far away from that point in either direction do not gain as much per win (going from 89 to 90 is more important than going from 69 to 70). In that sense, each marginal win for the Pirates (who figure to be way lower than that sweet spot) is really worth a fair amount less than it is to the average team. I'm not in the best position to say how much less they should be willing to pay, but it means that Iwamura's 2010 salary will not be nearly the bargain that it would otherwise appear to be. He would be worth more to a good Pirate squad, but the Pirates don't appear to be there in the only season for which Iwamura is signed.
The other main issue is that even if Iwamura is worth more than his salary, there may be other better uses for that money. Specifically they would probably have been better off spreading some of that money around to get some more draft picks signed. Also I would rather them spend money on someone who might have a decent chance to contribute to a winning Pirate team.
Of course I haven't said much of Jesse Chavez whom the Pirates gave up. The reason is because Chavez frankly isn't that valuable. As a rookie he posted a 4.85 FIP and 5.48 tRA (which is about 5.04 on an ERA-scale). Don't be fooled by his "good" ERA or WHIP; Chavez was replacement-level or worse in 2009 (he was 0.4 wins BELOW replacement level according to WAR). He's already 26, so he likely has some room for improvement but not a ton. I don't want to put too much emphasis on only about 67 innings of work, but Chavez would need to show a lot of improvement just to be OK. Good relievers don't have nearly the value that good players elsewhere do, and Chavez was not even a good reliever last year. The fact that he is under team-control for 5 more seasons isn't that big of a deal if he struggles to be far above replacement-level.
Overall the Pirates gave up very little to get a solid Major League player who is being paid below market value. Iwamura will help them win more in 2010 than they otherwise would have won. However, that money could have been put to better use for players that would help a competitive Pirate team. Overall that seems to make the deal pretty much a wash, not much to be that excited or upset about.