PageKeepers: Anyone Know About These?

While scrolling through BoingBoing late last night, I saw this review for the PageKeeper – which claims to keep your page in any book.  It looks like some kind of a clip with a spring component that basically clutches the back of the book and marks whatever page you’re reading at the time.

Does anyone have experience with these, and do they really work as well as the site claims?  Sad confession – I’m a dog-ear page-saver from way back (and shameless, so it’s probably too late for me there) but this looks like an interesting item and I’d love to hear if anyone has seen or used them.

As a side note: I’m guessing they won’t work all that well with my Kindle.