There has been a lot of chit chat about what ppl can and cant do in others yards. I've tested a lot of streets so far I can:
Harvest your meat and CAN pick up your meat collector
Harvest your milk and CAN pick up your milk collector
I cannot collect Hooch but I CAN take distiller if I ahve a key and I CAN distill for you
I can harvest all ore
I can harvest,pet,poisen and water all trees
I CAN nourish,water or HARVEST any crops left or right of houses.
I can harvest fireflies, jelli and barnacle and loam.
I can use your machines but I cannot take them.
I can use your icons but I cannot take them.
I can capture your pigs and apply youth potion to your animals
Edit: Keyholders of your old homes CAN get into your new homes and they can also disassemble machines.
I've heard it's a bug that is preventing ppl from harvesting other ppls crops. I hope this is a bug that isn't fixed.