I think it is useful to know how many people they have to turn down. It may just be a London thing but I know loads of people who are really worried about getting thier kids in to the Primary even though they are in the catchment.
Also ask about the ethos of the school what in a nutshell are they aiming to do with the kids - what outcome are they trying to attain. I asked this of one school and it tripped off the junior heads tongue. He was really clear that his aim was to support the development of high self esteem and confidence - primarily, the academics were important but not the be all and end all.
You could ask ratios of english as first language etc and whether the demographics are reflective of the area. Some appear not to be which is a bit wierd.
Are they planning any major changes in the next year - buidlings, grants from local authority. How active and successful is the PTA - usually a good sign if positive.