Original Review:
This product is essentially two very flat speakers, but not that different from those in your headphones, inserted into a rectangular pocket of foam. There are hard pieces in the pillow speaker, but there is enough foam in front of it, that you can sleep on it comfortably, as the back of the speaker just presses further into your pillow.
I cannot use this underneath my pillow as I have a tempurpedic memory foam pillow - its just too dense to hear the speaker well even at the highest volume - but a regular pillow would work much better.
However, I put this right on top of my pillow and put my ear on top of it, it works great, I tend to keep it at the highest volume and just adjust the distance of the pillow to my ear depending on how loud I want to perceive it, the speakers do not have a volume on them (that would be a nice feature). I've slept on this every night for 7 months and no visible wear or tear has appeared.
The only drawback is that the pillow has two plastic tabs similar the small end of a plastic tag holder that holds a price tag to your new clothes on the front, and that scratches my face, I cut it off though with no apparent repercussions, I'm not sure what purpose they served, perhaps to hold wires in place.
Overall, this is exactly what I was looking for as I need to listen to something to fall asleep, but with kids and husband often sleeping in the same room, I don't want to play it on a regular speaker.
UPDATE 11/7/2011:
So I originally purchased these speakers in 2007. I have used a pillowsonic speaker every single night to fall asleep since then. Unfortunately I'd love to say that my original pillowsonic speaker is still going strong, but that's not the case. I don't remember the exact timeline, but after a while the original speaker ended up with one of the wires going to one of the speakers detaching, so only 1/2 worked, then eventually it quit altogether. I purchased another one and it had the same eventual problem. I'm now on my third. However, this is over 4 years of literally laying on the pillow speaker (because as I said above, I can't put it under my pillow) all night long and the speaker gets yanked around by the cord a lot and shoved into pillowcases and suitcases for travel. Listening to an audio book to fall asleep is just about the only thing I have found that works for my insomnia.
So, although I've had to replace it a couple times, I am not displeased with the amount of time each has lasted, given the price and how hard I am on them.