I know electricity has been discussed elsewhere, but I was wondering if there's anyone is up for electricity in DF.
First it would be a nice requirement that Aluminum can only be processed in an Electric Forge. It could be used like a magma-furnace.
Electricity would be produced by a generator, which would require blocks, copper (aluminum/silver/gold) wire, mechanisms, etc. It would have to be connected up to a waterwheel or windmill (or a gear/axle) and would take all its power and turn it into amps (for simplicity). Too many amps in a single conductive line would cause the wires to melt, which would set things on fire or melt them until it's cooled or quenched. If it's kept connected (IE in a magma safe conduit) it will hit its boiling point and melt anything that has a lower melting point than its boiling point, beyond this the gas should be like magma-mist and be an insta-kill until it cools.
Electricity could be used in traps, either by causing something to melt and hitting a enemy with boiling metal, or be used to electrocute something (providing it has thin skin, or a heart to fibrillate for that matter). It could also be used as a power source for forges, but would require a lot of electricity to keep running.
An alternate source of power could be the creation of large galvanic batteries; insulated rooms with dissimilar metals and the room flooded with salt water, or if necessary Dwarven Wine. These batteries would slowly degrade the metals inside and would have to be drained and remade to continue providing power. Too much draw on the battery would cause the liquid inside to boil and produce poisonous gas (chlorine gas for example).
It would also pave way for lightning, which could strike and kill dwarves when it's raining, but could also randomly produce raw-glass if it hits sand, or could electrify an object (or body of water).
The risks of electricity would be: overloading your wiring and melting your base. Not insulating your wiring and electrifying a steel wall, floor or something. Not insulating your wiring and electrifying your water source (wouldn't damage your wells, unless they're made conductive, but would paralyze any dwarves drinking within the electrocuted area). Similarly conductive ground could be a danger. Building your base in an area with conductive soil could mean random electrocutions. You'd have to be careful laying exposed wires as a trail of ores like magnetite/electronium and other metallic ores could lead a path to either water, or a structure.
Finally electricity could be used in any religious plans in the future. Make a gold-plated statue and connect it to a weak electrical source (a generator run off of a low-wind windmill or an overloaded waterwheel, or a weak battery) and use it to make your dwarves feel the 'touch of god'.
I'm sure others around here could think of good uses for electricity in the game that wouldn't be unsuitable considering the presence of Adamantine, Magma casting, etc. If you choose to ignore electricity in your game, you would only have minor side effects (such as the random lightning strike) from the change. It would also enable a new attack type in our enemies.
For the very last I reference you to Frankenstein, and say good day at the possibilities of Monster Crafting!