It's not just scientific evidence: it's neuroscientific evidence!
If you're just interested in the takeaway from this article, here it is: spaced repetition works. We've known that it works for a long time.
If you want to use this in your learning endeavors, I recommend checking out Anki, an open source flash card tool that uses spaced repetition.
The takeaway I had was much different. They did not seek to demonstrate that it worked. They sought to explain how, at the neuron level.
+1 for recommending Anki; it's a fantastic tool for learning new subjects as long you can find a well-prepared deck. :)
I agree that some decks are a bit messy. I usually just make my own. It doesn't take that long, and I figure it's a good excuse to review and distill the information anyhow.