Just to add to what Matthew talked about below...
With a statistic like this, where you're looking at guys having ~between 100 and 200 opportunities a year, you'll want to look at several seasons' worth of data in order to get a more accurate picture of how good or bad they really are. One season just doesn't tell you very much about a guy's arm. It can give you an approximate idea of how well he performed at the time, but if you're trying to figure out a player's true talent level - which is usually what we're going for - then you need to expand your viewing window.
So with that in mind, let's look at a few interesting players:
- Ichiro had yet another season of being solidly above average, in both center and right. Since 2004, he has a 141 Kill+ and 117 Hold+ in CF, and a 118 Kill+ and 111 Hold+ in RF. I don't know if the inflated kill rate when playing in the middle is real, but those are impressive hold rates. People don't run on Ichiro. He has a reputation as being powerful and lethally accurate, and while the latter is a little bit of an exaggeration, he throws just enough runners out every year to deter many others from trying. This is just another of his many valuable skills.
- Franklin Gutierrez had a reasonable year last year, finishing just above the average in both categories. However, he was below average in limited trials in 2006 and 2007, so I wouldn't go too crazy just yet. The good news is that we didn't get him for his arm. We got him for his legs. Anything else he contributes in the field will just be a bonus.
- Adam Dunn hasn't posted a Kill+ above 75 since 2004, and he hasn't posted a Hold+ above 97 since 2005. Arm ratings aren't yet included in the UZR available on Fangraphs, so if you find yourself looking at Dunn's player page, you might as well subtract four or five more runs from his overall value in the field. He really ought to get over his pride and just donate his glove to charity or, failing that, a group of pioneers trapped in the Sierra Nevadas. They could put it to better use.
- Raul Ibanez has been posting good kill rates since the beginning of this statistic. He doesn't have the strongest arm in the world, but he has an accurate one. Not everything he does in the field is a disaster.
- Brian Giles has as much power left in his arm as he has left in his bat.