The production rate depends on your hashs per second and the probability of 1 hash to be the right one.
so basically khash/s * luck factor = generaterd bitcoins.
Given the current jump in ‘difficulty’ at around 875 khash/s I should be generating a block every 2.8 days.
So, no complaints… yet. 😄
http://www.alloscomp.com/bitcoin/calculator.php