Today and for the next few days until difficulty changes, which is currently 567358, statistical expectation for 1 Ghps mining rig is to earn 1.77 BTC.
Thanks for that. That's 1.77 BTC/day I assume.
I was considering your offer but I think I'm about to miss the boat:
1.77 BTC today, with the mtgox market at $18/BTC and 0.609 GBP/USD, is equivalent to 1.77 * 18 * 0.609 = 19.40 GBP. That makes for 19.40 * 30 = 582 GBP/month. Not very bad indeed.
But as soon as difficulty increases so that the reward gets as low as 1.22 BTC/day, earnings will be 1.22 * 18 * 0.609 * 30 = 401.208 GBP/month, which is essentially the same as the cost, thus killing the benefit. Yes, mtgox and GBPUSD will change, and they may make matters better or worse—that's beyond anyone's control though.
Mind you, I'm not trying to troll and I might be radically wrong at some point, in which case I'd be grateful if you (or anyone) pointed me where. But I honestly think it's not very wise to join this now... which is a pity.