Like everyone else I've been pleasantly surprised by Walker's progression this year after having essentially written him off.  I've only watched a handle of games in full since his call-up, but have been particularly impressed with his play in the field considering his lack of experience at the position, from what I've managed to catch he's looked consistently competent at the position, and has a made a handful of great plays by virtue of his athletic ability.  I'm curious though to hear what everyone's impression have been and what sort of upside you think he has defensively, especially those who have caught a few more games than I.