Utility (accepted shares / min): 0.14/min
That's approximately 7 Minutes for ONE accepted share. If you watch the bitcoin monitor for a while ...
... then you may notice that's almost the rate blocks get generated.
Also, a block per 10 minutes is the target generation rate regulated by the difficulty setting.
Anyway, I'm not good with statistics, but the current difficulty, 1888786.7053531, is the number of shares you need to calculate on average to find a block. So CPU mining is really pointless at this difficulty level. Maybe if everyone was to turn off their GPUs...