Aaron Gleeman from Rotoworld thinks the change won't impact much:
No doubt looking to find some cure for whatever ails Carlos Zambrano, manager Lou Piniella said Sunday that the Cubs may make Henry Blanco the struggling ace's "personal catcher." Zambrano has a 3.27 ERA with Blanco behind the plate, compared to a 7.07 ERA with Michael Barrett catching for him, but that's unlikely to be the cause of his struggles. Plus, lost in the nice-looking ERA is that opponents have slugged .447 against Zambrano with Blanco catching.
Whether statistical or visual, various evidence points to some kind of arm problem causing Zambrano to pitch at less than full capacity. Zambrano is missing somewhere between 3-5 miles per hour on his fastball, typically working in the 90-92 range of late, and an examination of his delivery shows some significant modifications. Given his huge workloads over the past five years, it certainly wouldn't be surprising to learn that arm soreness is behind the changes.
He put together a strong start Saturday against the Dodgers, but Zambrano remains a huge question mark. His strikeouts and velocity are down, he's no longer an extreme ground-ball pitcher, and Zambrano is on pace to set a new career-high in homers allowed by the All-Star break. As for the personal catcher issue, it's worth noting that Zambrano held opponents to a .204 batting average with Barrett calling pitches for him last season. That's not the problem.