As per this thread, I think it would be very useful to have a setup designed manufacture supercharged creepers in large amounts, then use them in mining.
How it would work:
1. A mob farm and sorter would spawn mobs and leave only the creepers.
2. creepers would be transported to 3x3 pens.
3. there would several pens in each chunk, and each would use BUDs to detect when lightning strikes in them.
4. when struck, a pen would place creepers in minecarts and deposit them in a central area, waiting for the player to store them in an unloaded chunk.
5. when ready for use, a single creeper could be deposited from the storage area, then taken to the location of the blast mine/victim/future slime farm.
This leaves the details of its realization, as well as the issue of how best to employ the creepers with accuracy and without getting killed. I'm going to work on my own attempt, although I'm hoping more talented players will hobble along and try their hand.
Addendum: I want a reliable means of launching charged creepers like missiles.
The problem is that unlike TNT creepers only explode when attacking an enemy, and call off the attack if you move far away too fast. It'd be too risky to trigger the thing yourself.
So what I'd do is first get the creeper to turn hostile against a skeleton by making it intercept an arrow meant for a player. Then drop the skeleton quickly, followed by the creeper, where you want the explosion to occur.
And Snow golems are still the best: Have them shoot zombies, and put creepers in the middle. Skeletons are harder to store, and less accurate.
Anyway, since this tread died, some developpement have been made. For exemple, JL2579 published a video of a full auto cobble harvester, using a mob spawner to get creepers, a cobble generator and a player in a minecart. Using this, you can go afk and come back with a full inventory of cobble.
Ok, have fun! To sort the creepers, use a cat and a big half-circle, with a hole in the way of the half-circle.
(When creepers see cats, they chose a block in a fairly large radius away from the cat and go there. So if there is an hole in the way, they will fall in)
To split the skellies, use snow golems shooting zombies to aggro every mobs to the snow golems. Only the skellies will chase the snow golems since the zombies will go after the villager you put somewhere near and the creepers will run from the cat. Just put a hole(with trapdoors) in the way of both the skellies and the zombies, and you'll have 3 groups