It worked well for us when DS was 3-4 months old. Lasted a month or so with realy good sleep, then the next 'thing' happened. DS had a lot of things... and nothing would have worked anyway. So, it was successful for us. Sort of.
This was pretty much my experience with it too. It's only been in the last few weeks that I've had the energy/motivation to be really strict with getting DD up at the same time every morning. We've always had the same bedtime, but our days could start any time between 7-11am. She's responded really well to having the same wake up time and has finally been sleeping through for a week now. I don't know if it would have worked earlier, but I know that we were both ready for it now. I think the best thing about Pantley is that there is no guilt if you do choose to do things in your own time.