When you can buy Antminers for half the price of CEX.IO "Ghashes", I think it should be self explanatory.
They also take their 'fee' for electricity out for the ghashes each time they deposit your fraction... which I suspect is probably inflated a bit.
For example (I decided to put about .35 BTC in just to see how blah it is) this is while I slept last night:
Block #292047, Reward: 0.00007085, Fee: 0.00000332
Block #292046, Reward: 0.00007093, Fee: 0.00003404
Block #292030, Reward: 0.00007318, Fee: 0.00001803
Block #292018, Reward: 0.00007215, Fee: 0.00002595
Block #292004, Reward: 0.00007213, Fee: 0.00000042
Block #292003, Reward: 0.00007480, Fee: 0.00000269
Block #292001, Reward: 0.00007211, Fee: 0.00001223
Block #291998, Reward: 0.00007463, Fee: 0.00000269
Block #291997, Reward: 0.00007197, Fee: 0.00000146
Block #291996, Reward: 0.00007193, Fee: 0.00000083
Block #291995, Reward: 0.00007211, Fee: 0.00000064
Block #291994, Reward: 0.00007196, Fee: 0.00004875
Block #291972, Reward: 0.00007204, Fee: 0.00000104
Block #291970, Reward: 0.00007330, Fee: 0.00000042
Block #291969, Reward: 0.00007331, Fee: 0.00000042
Block #291967, Reward: 0.00007185, Fee: 0.00000044
Block #291966, Reward: 0.00007450, Fee: 0.00000251
Block #291963, Reward: 0.00007213, Fee: 0.00000042
Block #291962, Reward: 0.00007227, Fee: 0.00000228
Block #291959, Reward: 0.00006049, Fee: 0.00001763
I also learned, you are not allowed to withdraw what you put in for the first 48 hours. I'm taking my bitcoin out as soon as they'll let me by selling the gashes.