FIP is a metric by which pitchers are judged based on how they pitch. Luck, defense, etc. are intended to be eliminated by the use of this metric. It takes into account how well a pitcher strikes out hitters, controls walks, etc. It is roughly analogous to ERA, though a better measure of how a pitcher is throwing.
Sox Starters, Descending order by FIP:
Justin Masterson: 5.16 FIP v. 3.61 ERA
Tim Wakefield: 4.85 FIP v. 3.77 ERA
Bartolo Colon: 4.45 FIP v. 4.09 ERA
Clay Buchholz: 4.18 FIP v. 5.94 ERA
Daisuke Matsuzaka: 4.18 FIP v. 3.04 ERA
Jon Lester: 3.57 FIP v. 3.14 ERA
Josh Beckett: 3.39 FIP v. 4.15 ERA
Beckett and Buch have been unlucky. Beckett's 4.7 K/BB should give him a leg up on the competition, but he's been allowing more HRs than he should be (1.09/9 IP) and his BABIP has been a bit higher (.324) than average (approx. .290-.300). I feel like even Buch's FIP is a bit low. He's been unlucky, but he also hasn't been great. He has, however, been better in terms of K/BB (1.91) than lucky Daisuke (1.47). This reinforced my feeling that Daisuke has actually been the harder one to watch on the mound. His % of runners LOB is about 10 higher than the league-average, and that walk rate (5.4 per 9) is downright scary. That particular house of cards could come crashing down any day now.
Masterson has also been very lucky. He's got similar problems to Daisuke, in that his LOB% is probably unsustainable. His HR rate is high, his BABIP is low (.232), and his K/BB makes me want to vomit (1.62). However, he's definitely still young, figuring it out, and his ability to get GBs has helped him out of jams. (I put him in the starter column, as the great majority of his innings are in that role)
Few pitchers match their FIP exactly, and Colon and Lester are good examples of pitchers who have been close enough to their FIP to not be deemed flukes in some way. Lester's FIP indicates that he's been a high-quality starter this season. And what have our eyes and traditional statistics told us? The same thing. Colon has looked like a league-average starter who's was reliable for us when pitching. His FIP indicates the same thing. By just the starters, Colon's K/BB is second-best among his teammates. Lester is actually 9th among 43 qualified AL starters in FIP.
Wakefield is the breaker of all rules, and to try to pin him down based on his FIP is probably pretty foolish. There are no comparisons for him, really. I'd say he might be a bit lucky, but to assume that in reality he's a 4.85 run pitcher seems wrong as well.
Sox Relievers, Descending order by FIP:
Mike Timlin: 4.41 FIP v. 5.34 ERA
Javy Lopez: 4.25 FIP v. 2.51 ERA
Hideki Okajima: 4.01 FIP v. 2.66 ERA
David Aardsma: 3.44 FIP v. 2.75 ERA
Manny Delcarmen: 3.34 FIP v. 4.05 ERA
Jonathan Papelbon: 1.94 FIP v. 2.05 ERA
Paps is awesome. His FIP is actually better than last season, despite seeming more human than ever in the last two years. His K/BB is a strong 8.14, and he's done a better job keeping the ball in the park. MDC, similarly, has improved on his FIP from last season (3.85) by also doing a better job keeping the ball in the park and improving his walk rate.
Oki? Well, the feeling that he would be something between last season and his horrendous start to this one is probably correct. I don't know that he's ever going to get back to how good he was last season; he was phenomenal. His BABIP (.294) is about right/average, and it has produced a somewhat predictable 1.34 WHIP. Surprisingly enough, his LOB% is higher than last season, which should shock most who've seen him let inherited runner after inherited runner score in tough situations this year.
Javy kind of sucks. I don't know how else to put it. 1.33 K/BB and a probably unsustainable LOB% of his own. Timlin, somewhat surprisingly, hasn't sucked as much as we might believe. To my own eyes, he's certainly pitched a lot better as of late, and could be more trustworthy than some (Lopez) in situations. Aardsma is kind of the enigma. His stunning ability to walk a lot of people made me believe his FIP would be higher than it is, but I suppose his second-best on the Sox K-rate (9.38/9 IP) has helped with that. He's also been very stingy with the longball, best on the Sox staff in that department. We'll see how it goes, but he's certainly worth keeping around for next season.