There should be a 51% attack. That would cause Bitcoin prices to temporarily plummet, so I can buy in cheap, then when the price recovers I can profit out and gain lots of money!

i agree, and not only that, but then big players and bitcoin figures would realise that their role must be much more serious.
another view would say that big pool like ghash should simply divide the load on two sides, thus halving their hashrate danger, while having same hash (just split on 2 parts)
i think anything that happens is gonna work just great for most of traders
