A few days ago on here, someone was claiming to calculate the income of a 5830, and he calmly stated what a months' income would be -- based on 877K difficulty!
(Newsflash, bro: that difficulty level expires in LESS THAN TWO DAYS! Sorry to burst your bubble)
So you won't get more than 2 days income at this difficulty -- and then you can't count on 1.3M difficulty either, because that will only last 8 or 9 days...
Those monthly income projections are so stupid. That's why you have people wanting to sell/return their mining hardware -- when reality comes a-calling.
Ok, bra...so whats different about the 5830, or any other card, troll? Now you show up here harping on the 5830.
Difficulty increases are across the board, whether the new miner with one 4650, or the super miner with 20 rigs of 4x 6990s. Everyone will be affected the same.
Mining for block generation is for the long haul, and correlates with both difficulty and price. Both can go up, and down, Captain Obvious.
It's called efficiency.