Ever since the Colorado Rockies have come into existence, there has been a discussion about what "type" of pitcher would succeed there. Going into what will be the Rockies' twentieth year of existence, the simplest answer to me seems to be "the good type," though it is a little more complicated than that. Talk that pitchers in Colorado should strike batters out and keep the ball on the ground is almost too basic - that's a recipe for success everywhere, not just in the Rocky Mountains. What needs to be clarified is that fly ball pitchers with middling strikeout rates won't necessarily fail everywhere, but Colorado is an especially bad fit.
Colorado, meet Jeremy Guthrie.
This is a rough break for Guthrie, who has actually been a better pitcher than I realized. In 2011, he lost 17 games for the second time in three years, but he was a solid rotation guy, compiling over 200 innings of averageness in a division where that's tough to do. In all five years with the Orioles, he had an ERA+ over 90, and pitched 175 innings. Three times he managed a 110 ERA+. In 2011, he had his third straight year over 200 innings. All this, despite never striking out more than 5.7 per nine innings, and a GB/FB ratio right around 1/1. It would be reasonable to think that moving out of the AL East would lead to an improvement in his win-loss record (47-65 in five years with a crummy Orioles team) and a bit more recognition.
What's important to note is, while Guthrie has been unlucky regarding his W/L record, he's been fairly lucky on balls in play and in keeping his fly balls in the park. His highest BABIP was the Orioles was .286, and less than 10% of his fly balls left the park. This is unlikely to hold up in Colorado. While you know about how the ball carries, an offshoot of that is that outfielders tend to play deeper, allowing more singles to fall in front of them. In 2011, a slightly down year for offense, Rocky pitchers had a .298 BABIP and allowed 11.6% of the fly balls to go out of the park.
So, while it's normal to expect any pitcher to have his numbers hurt moving to Colorado, Guthrie, who strikes out a below average number (and therefore allows more pitches to be hit) and has a below average ground ball rate (therefore meaning that more of those pitches that are hit go up in the air), is probably more susceptible to the dangers of Coors Field than most pitchers. \
Guthrie turns 33 the first week of the season, so it's unlikely his pitching is going to fundamentally change. He should strike out some more guys, because he'll be facing NL West pitchers instead of AL East designated hitters. (Coors field may be intimidating, but I think he'll prefer pitching to Tim Lincecum there to David Ortiz in Camden Yards. Having to bat against Tim Lincecum, on the other hand...) Still, even with a slightly improved strikeout rate, his fly ball tendencies and low K rate will probably mean a higher ERA. A little bad luck could make for a very ugly stat line.
In return, the Orioles received Jason Hammel and Matt Lindstrom. I'm not sure Guthrie is all that likely to outperform Hammel (though Guthrie's durability has value), and Lindstrom had a nice year out of the Coloardo bullpen. Guthrie will make $8.2M in 2012, Hammel and Lindstrom about $8.3M combined. In 2011, baseball-reference had Hammel and Lindstrom worth a combine 5.2 WAR, while Guthrie was 4.5 WAR.
Hammel was once a pretty big prospect in the Tampa Bay system. In 2006, Baseball America had him rated #79 in baseball. This was just before the real influx of talent two years later. Traded to the Rockies after the 2008 season, he's had three straight years in Colorado with ERAs in the mid 4's and 170+ innings. His strikeout ratio plummeted from 7.1 in 2010 to 5.0 in 2011, so that's the main thing to keep an eye on. He's only 29, so a rebound in his strikeout rate could lead to him outperforming Guthrie.
Lindstrom spent a chunk of 2010 as Houston's closer, saving 23 games, but he was much better with Colorado in 2010, cutting his ERA by a run and a half, based largely on lowering his walk and home run rates. He'll be in the Oriole bullpen, and he'll probably be just fine.