Worked well for us with our son, within a few days. Doesn't mean he never wakes now, he often wakes for a few minutes, cries and goes back to sleep (all within 5 minutes or less) but it just means when he does cry for a longer period, we're actually more likely to pick up on potential problems.
The thing that always concerns me most in this debate is that supposed "scientific facts" are thrown about carelessly.
The AskDrSears web page that's linked to is a case in point. If you take a quick look through the references to back up that article many of them are dubious at best. The first is a Masters thesis, another is about development in rats, and even those about human development mostly refer to "persistent crying" as a symptom of other problems, not as the cause. For example, "Persistent Infant Crying and Hyperactivity Problems in Middle Childhood" is an article about children who are reported to medical professionals as having problem crying. That's isn't the same as controlled crying, where a parent has deliberately allowed their child to cry for a short period.
Their stated conclusion was that children referred medically for problem crying and associated sleep problems are more likely to have hyperactivity problems in later life.
Another referenced article, "Long term cognitive development in children with prolonged crying" comes to similar conclusions from a similar starting point - "excessive, uncontrolled crying that persists beyond 3 months of age in infants without other signs of neurological damage may be a marker for cognitive deficits during childhood. Such infants need to be examined and followed up more intensively."
So in both cases we've discovered that problem crying persisting for 3 months or more might indicate deeper problems.
So neither of these articles (I haven't read all of them) provide the slightest evidence that controlled crying causes harm to children. Similarly, there are no major studies on the effects of cortisol on babies, though I'd be interested to be directed to any that I've missed.
I'm not an expert, nor do I castigate people who use one approach or the other, but I think there's a lot of misinformation about this subject based on people's more general perspectives on child-rearing, and unfortunatley a lot of people might be put off controlled crying, or else do it and feel guilty that they're harming their children.
My little boy is 9 months old and sleeps from around 7pm until 6-7am most nights. We used controlled crying several months ago. To each their own.