Dwarvization of obsidian industry = make it into a trap. Muahahahahaha.
Basically (and i already posted this in another thread) you carve out a big pit. Say 10x30xasdeepasyoucan, except for the first and second (highest) level of your pit being 8x28.
This (highest) level will be "floored" with (retractable) bauxite bridges (two 8x9's with in the middle an 8x10) linked to an awesomely colored lever (preferably purple).
This room will obviously be filled with magma.
The room beneath it will be floored with again 3 (retractable) bridges (preferably of a cool expensive material), this is your entrance granting you and everyone, umm, entrance to your fortress. These 3 bridges will again be linked to your awesome lever. One level beneath it, the third level, will again be floored with bridges (make them blue or whatever) now though three 10x10 ones, these bridges do not need to be linked (they will be destroyed in the process) Fill this room with water.
Wait till nasties (meaning elves, racoons, fluffy things... and most of all every immigrant who as much as contemplate about daring to bring along a cat/kitten) enters your entrance, pull awesome lever, watch them get solidified in mid air while your miners, after having sharpened their picks, wait till the whole slab of obsidian finally touches the bottom level after which they will happily mine the whole thing looking for fun surprises (they sometimes make bets you know, apart from the annual "mine yourself an elf" contest, keeping spirits high). You only need to rebuild the waterholding bridges before making them, um, hold water, which is done in a jiffy seeing that you don't need to link them up or anything (and obviously refill the magma room after having switches back the awesome lever, ready to do its purpose next time)