so, as i see it; if multiple user have the same private key and they try to make a transaction to another wallet - the one whose transactions are mined first, gets it? the first one will be the one who splits it in the smallest transactions; but in the end transaction costs will be higher than the transaction amount?
it's a mess - huge waste of time
I dont know - it worth observing peoples behaviour at the very least.
Unless you are manually hacking transactions together to get a decent single output I dont think you will make anything out of this. If you are too granular then fee's will eat it all up. I managed to cobble a few tx's with ~70 inputs each, but with a decent fee to ensure it got through ( early ones took 2 hours to appear in a block, some a lot longer) it wasn't worth the effort of writing the script.
Still, I've learned some cool 'hidden features' in bitcoind.

That, and my php's gone to shot.