Amazon’s Kindle Matchbook program was released overnight. You can now check and see what print books that you have purchased in the past participate and what the discount is to also pick up the Kindle Edition of that book.
The discounts range from free to $2.99 to get the Kindle Edition. When I looked, I only had 6 books that were participating. But I also have not purchased a lot of print books from Amazon.
You can also search for print books that have Matchbook discounts (for instance if you are giving away a print book and then want to keep a copy of the kindle edition for yourself). I did notice that many of the books that were marked as Kindle Matchbook compatible in the search were not showing up that way when I actually looked at the book. So the rollout may be a bit slow. Right now Amazon has just under 75,000 book that are Matchbook compatible according to the search.