I've recently finished building an iron golem farm at the top of my mob spawner tower. The first floor of the farm is at y=242. I'm using Docm77's basic iron farm design, but I haven't gotten any drops yet, after playing nearby for at least an hour.
Is there a height limit at which Golems will spawn? Are they despawning before they get killed? (I'm playing between y=64 and y=100, mostly [I didn't think Iron Golems despawned though])
Edit: this farm works fine at lower levels. I had one in this very world in this very area, but I moved it because I didn't like where it was. The only difference is that it's so high. I've built one at the same exact height in my creative world, and there are no spawns from that either, after AFK-ing for about an hour.