"While watching the Leonid shower I had an idea for space mining. One of the main arguments against mining asteroids is that it would cost too much to bring the stuff back to Earth. My thought is why fly it back when you can just drop it. The asteroid could be cut into small chunks (5'x5', 10'x10', 20'x20', or what ever) by high power lasers like blocks from a quarry. Brought back to Earth orbit and simply dropped from orbit to re-enter the atmosphere in a deserted location. While some of the block would be lost due to friction, most of it would remain intact and make it to the ground and a recovery vehicle could pick it up for processing. I'm not sure if this approach has been thought of before, but it seems to be a simple idea."

Hmm, well I have mentioned s/g similar but I was thinking of more finished products- things like ingots of Aluminum or things like big structures "delivered" to some remote site on Earth- but I wasn't thinking of near term applications.
I don't think there is any sense to bring material from Space to Earth when the "price" of anything useful would be higher in Space environment then on Earth. In other words such things as a kilowatt of power is worth more in orbit than on anywhere on Earth or water, or rocket fuel, or anything that is needed in space.
The exception of this would be those things which are collectables or needed for scientific purposes- e.g. rocks or dirt from the Moon, NEOs, or Mars. Currently theses thing are worth somewhere around $1000 per gram, and at that kind of price well worth bringing back to Earth.
As far as cutting space rocks into blocks, there are a number of problems with this. First is the practiablity of using lasers to get chunks of space rocks (need a lot of energy, would be fairly slow and with uncertain results- compared to simply using a few sticks of dynamite).
Next there is the problem of moving these chunks to intercept Earth. if these chunks are entering Earth atmosphere at a high velocity then they could explode in the atmosphere- like dozens of rocks are doing each year (your 20'x20' chunks could possibly remain intact enough to impact the Earth surface- similar the a nuclear bomb).
Finally what is the value of these chunks if you could deliver them somewhat intact and to a very precise location (this is a very tall order).
For collectable or research really huge quantities aren't needed- one 10' cube would probably easily satisify world demand.