At the current difficulty level, even my home computer is able to pull in about $1,500/yr in profit. After the next increase, it's going to drop to an estimated $910/yr in profit.
Extrapolating profit from any difficulty level out to an entire year doesn't make any sense at all. Each difficulty period only lasts about ~10 days while difficulty is increasing.
1-2 months from now, you may very well be losing money by running your video card due to electricity costs and cooling costs if you're particularly unlucky.
I thought it was silly to project MONTHLY income. It's downright insane to project YEARLY. Bitcoin might not even BE HERE for a year...