I am going to try to pick interesting cases: players who were injured, or had (seemingly) fluke productive or unproductive seasons. For outside forecasting, I'm including PECOTA, Marcels, ZiPS, Bill James, and CHONE forecasting systems, as well as a quick and dirty method of my own to attempt to project 2007 performance. Anyone reading this who has read me before would probably guess that my method uses batted-ball data, and you would be correct.
With an assist from Eric Simon of Mets Geek and Amazin' Avenue, I've got myself a nifty spreadsheet that corrects players' batting lines for the difference between their Batting Average on Balls in Play and their expected Batting Average on Balls in Play. The need for a spreadsheet comes in with the adjustment made to this; when you add in the difference to the batting lines, every extra or missing hit is counted as a single. Eric tweaked it so that the extra SLG points are distributed according to their hit-type rates, meaning a few extra points for extra-base hits. For many players there will not be any difference, but it will help to correct slugging percentage for a few players on either end of the extremes.
Dan Uggla hit .282/.339/.480 in 2006, coming out of nowhere to enter a bid for the Jackie Robinson Award after replacing Pokey Reese in spring training. Uggla had hit .297/.378/.502 in Double-A Tennessee in 2005, which looks impressive until you realize he was 25 years old already. His age 26 season went fairly well at the major league level, and his better months were spread throughout the season a bit.
Uggla was fairly lucky though, as you can see from the BTBS line in the table. He was .027 over his expected BABIP, given his line drive percentage; sadly, we don't have his minor league batted-ball data at the moment, so it's tough to gauge whether or not his 16.8% line drive rate is normal or low for him (generally, around 20% is average). Marcel and James are fairly optimistic about Uggla repeating his 2006 season, while the rest of the forecasts--and the BTBS correction for 2006--are a bit more pessimistic. I feel comfortable with the lower ones, although Uggla has shocked us once already.
Josh Barfield hit .280/.313/.423 in his rookie season in San Diego before being dealt to the Cleveland Indians in a deal centered around Kevin Kouzmanoff. I'm somewhat surprised at the pessimistic forecasts thrown out by most of these systems, since Barfield's major league equivalent line from 2006 was .290/.329/.442, and he wasn't incredibly lucky or anything. Considering his power isn't that high yet, he should try adding some plate patience to his repertoire.
One question surrounding Barfield is his defense: some systems (like FRAA) are big fans, while David Pinto's Probabilistic Model of Range thinks he's fairly average. The Indians should hope that FRAA has the correct assessment here, because if Barfield's bat does stay at the level these forecasting systems indicate then they may not be pleased with his production. I'm of the mind that he'll beat these projections, and I know a few people who really like him that I trust. His upper level PECOTA percentiles are much more optimistic than his weighted mean.
PMR likes Giles about as much as Barfield, so there's probably no real difference between them defensively, at least according to this system. Giles used to be more of a plus fielder, but his range has decreased with age. Before the 2006 season, Kevin Goldstein wrote in Baseball America Prospect Handbook 2006 that Barfield had "made strides defensively and is no longer expected to have to move to left field," which should explain his defensive abilities somewhat. In the long run the Indians will like having Barfield more than the Padres like having Giles around (if they are to re-sign him anyways), but they are two teams in different places. The Indians are reloading with kids to match up with the players on the roster hitting their peak, while the Padres are the team with one of the worst minor league systems around; they're playing to win now with a somewhat older core of players in a winnable division.