I do a variation that I call Whinge it Out. I am not an advocate of CIO because I really cant stant to hear my baby cry, but I am ok with listening to her grizzle and whinge while she is dropping off to sleep. Any sign of distress and I'm a big mumma bear rushing back in to grab my baby up.

I think it all depends on whether your child has clearly distinct cries and whether you can distinguish between them. My bub rarely ever gets into the 'distressed' range (and I'm a mess when she goes there so I don't know how you mum's out there cope if you get it everyday), does mostly low grade grizzling which I ignore if DD is playing with a toy when I peek in, and a protest cry that I do tend to respond to as I figure she's not quite ready for that sleep afterall.

I also find that going through the sleep routine as soon as I see the first sign of tiredness works for us too, as DD gets a feed, and then the blinds go down etc and by the time thats done, she's really ready for a sleep.