I have been thinking about moving to digital books instead of physical books for all my "programming" related books from here on out and seems like the kindle service has the best cross-platform service. Now I do plan on buy an iPad eventually (probably going to wait until the next release) but have a question more about the kindle service. If I start buying books through Kindle on my Mac, when I eventually get an iPad, will I be able to transfers all my books over without having to pay again?