kara - I used to use one. It was my last resort if he was super fussy. I'd flip him on his side and he'd be out like a light. So even now he likes to sleep on his side, but only his R. side. He will sleep on his back. I stopped using the positioning a few months ago when he started being able to roll on his own. I'm slowing trying to phase out all the props (positioner, swaddle) soother is the last one and he can almost get it back in on his own now so I'm leaving it.
Jenn - My LO is different, 2 hrs in the AM, 3 hrs in the afternoon, and 4 hrs before bed. He has the biggest yawn ever that he just cannot stifle no matter how hard he tries. So he's pretty easy in terms of sleepy cues to read. It is so hard to find that sweet spot. In the middle time I'd say he's getting tired around 2:30 and then change diaper, sleep sac, read a book, and into bed so it's usually 15' from when I see he's tired to him being in his crib and another 5-10' until he's asleep. I've read it takes 20' on average for babies to fall asleep so it's just trial and error to find that perfect A time... and then it all changes!