The +/- is determined by the percentage of plays that are made over a given distance (the plays are broken into bins by distance and, I believe, direction) league-wide, how many plays an average fielder would have made give the number of grounders or flies hit to a given bin under a particular fielder's watch, and how many plays the fielder actually made. In that setup (UZR is a little different, but I'm not sure how or where), the space of the outfield may magnify a negative or positive reading, but it won't make an above-average fielder look below average. (Playing half your games at an altitude might, however, but that's a discussion which doesn't directly affect the Mets.) At any rate, there should not be a significant park effect for infielders, at least that I'm aware of (without artificial turf affecting things anymore). Reyes certainly passed the eyeball test, but Jeter has made a career out of doing that, and I saw Elvis Andrus make a number of plays in the postseason that I don't think Reyes makes. On the whole, there wasn't that much disagreement between UZR and +/- regarding the Mets, with the exception being Angel Pagan. UZR had him going from extremely positive in 2010 to extremely negative in 2011, while the +/- had him going from solidly positive to a -1. The eyeball test certainly had me thinking he was a step or two slower than last year, but the UZR difference seems extreme to me.