I don't mean to go all-Rangers on you, but I do find Julio Borbon to be a fascinating case. Here is my take on him.
Not a Rookie: Julio Borbon
Julio Borbon was drafted by the Rangers in the supplemental first round in 2007, from the University of Tennessee. Highly-regarded for his speed and athleticism, he was considered somewhat raw for a college player, especially with his plate discipline. He hit .345/.370/.506 in 40 games for the Volunteers, missing the early part of the season recovering from a broken ankle. He stole 10 bases in 13 attempts, but drew only six walks against 20 strikeouts in 174 at-bats. He got into nine games as a pro, two rookie ball contests and seven games for Spokane in the Northwest League, hitting .189/.250/.216. I gave him a Grade C+ in the 2008 book due to his athleticism and draft position, but I was somewhat skeptical about his bat. I wrote "I don't have a good intuitive feeling for Borbon, and personally I think he's going to be more of a fourth outfielder type" than a regular.
I tend to trust my intuition about such things, not for any mystical reason but because "intuitive feelings" are (in my opinion) often a form of subconscious pattern recognition and information processing. In college, Borbon looked to me like a guy who was getting by on sheer talent, but lacked the refinement and polish for his tools to translate well to the pro level. However, in this case it looks like my intuition was wrong.
Borbon began 2008 with Class A Bakersfield in the California League, hitting .306/.346/.395 in 66 games with 36 steals in 43 attempts. His walk rate wasn't great with just 15, but he fanned only 30 times in 291 at-bats while hitting 20 doubles. Promoted to Double-A Frisco at mid-season, he hit .337/.380/.459 in 60 games with 17 steals in 28 attempts. His plate discipline wasn't much better in Double-A, but he showed more power.
Borbon went to the Arizona Fall League that year and worked hard to improve his strike zone judgment, focusing on working the count. This was obvious: he looked like a much different player in Arizona compared to Frisco in terms of approach: he wasn't swinging at everything and was doing a better job laying off junk he couldn't hit. Statistically this resulted in 17 walks in 96 plate appearances in Arizona, a huge improvement. I gave him a Grade B in the '09 book, writing that while he needed another year in the minors, "I see him now as a regular major league center fielder, not just a fourth outfielder" due to the improved strike zone judgment.
Borbon began '09 in Triple-A Oklahoma City, hitting .310/.370/.388 in 96 games, with 25 steals in 32 attempts. He maintained some of the discipline he developed in Arizona, drawing 33 passes against 40 strikeouts in 407 at-bats. . .not a great walk rate, but better than before. Promoted to Texas for the stretch, he hit .312/.376/.414 with 19 steals in 23 attempts, drawing 15 walks against 28 strikeouts in 157 at-bats.
The 48-game sample size in the majors shows some interesting data; including a hard platoon split (.333/.401/.447 against right-handers, .125/.125/.125 against lefties). He had a sharp platoon split in the minors (.805 OPS against right-handers, .675 against lefties in 984 career at-bats), so the major league data wasn't a total fluke. I think this is something that may improve in time, but it's possible that he'll need a platoon partner if it doesn't. He also had a big home/road discrepancy (.400/.440/.514 at home, 241/.327/.333 on the road) in the majors. However, given the sample sizes involved I'm not sure we can draw any really broad conclusions about the home/road split.
Fangraphs indicates positive performance against fastballs and sliders, but some struggles against curves and changeups. His strikeout rate rose in the majors, but his walk rate was okay and the K-rate didn't get out of bounds in absolute terms. On defense, the major league sample size is too small for the UZR numbers to mean much, but in the minors he posted outstanding Total Zone numbers, which matches scouting reports about terrific range.
Overall, from looking at the numbers and from watching him play over the last three years, I think Borbon's improved polish since college is legitimate. His swing hasn't changed much that I can detect; he's just a bit more selective now about what he swings at. I expect that he'll be a consistent .280-.300+ hitter, with plenty of steals, gradually improving his plate discipline and walk rate, and excellent outfield defense. If he was still a prospect I'd give him a B+. This is a player who added some skills to go with his tools.