We are likely already there. 25 terrahashes is my conservative estimate..  http://www.coinchoose.com/

The gpu miners have been conned into the alt-coins, very much the same way that the Asic Dream did. Just hearing them all trumpeting the promises of whatever crypto-currencey god(s) they believe in, makes me want to throw up. More now because I've learn that 1-2 of those alts are starting up a ... (pardon my foul mouth) BANK.

@SirMintALot

Is there any evidence of collusion between the big three ?

What is to stop them from merging ?