With all the machines in Industrial Craft, it's very handy to be able to move items between inventories automatically. Vanilla MC has the hopper, but it has limitations, such as an inability to go up and a relatively slow speed. Buildcraft has a similar block, the Chute, which is faster but has more limitations (it can only accept items from pipes and manual transfers).
So I propose that Industrial Craft has its own variant, the Conveyor Belt. Each block of belt has an internal inventory, like hoppers. Unlike hoppers, conveyor belts can go in all six directions, just like the production lines in factories. The belts are powered by a motor, which sends a pulse down the line that activates the belts and has them move their items along (this means that only the motor needs to be powered, not the whole line). The motor block is an inline block, that is, it has a conveyor belt as well as having a motor, so it's placed in the belt path. Each belt block outputs to one side (to prevent branching) and draws items from inventories on all the other sides. Since the items are stored inside the block inventories, lag is low and they are not displayed outside moving along unless the developers actually feel like programming that in.
Technical information aside, the usage of the belt would be simple. Say you wanted to set up a simple production line: ores to macerate, then smelt. You first set up a chest that holds the ores. Belt 1 then connects from the chest to the Macerator. Belt 2 connects from the Macerator to the furnace. Belt 3 connects from the furnace to the chest that holds the final ingots. If done with hoppers, this would have to be built in a stairstep manner, as hoppers only remove items from the block above them; also, you would be limited to how fast the hoppers could, well, hop. This could also be done in Buildcraft, but it wouldn't be very compact and you might not have Buildcraft. Conveyor belts would be more compact and would not require an additional mod.
The primary downside to conveyor belts compared to hoppers and buildcraft wooden pipes and engines is that the belts must be powered. However, they wouldn't require very much, and can be made faster than their unpowered counterparts. After all, buildcraft wooden pipes and engines are slower than hoppers, and if you want more speed you have to increase to stone engines anyway. Here we're just putting it in Industrialcraft instead!