Did you get an iPhone 5 today?
We're jealous - ours hasn't arrived yet, and we got our order in just a bit too late to be in today's batch. We're looking forward to using Eucalyptus on ours when it does arrive just as much as you are though.
The current version of Eucalyptus was, you might have noticed, recently updated for iOS 6. This is the version of iOS that's on the new iPhone 5, so it should work very well. You'll notice when you use it, though, that the book pages are the same size as they were on old iPhone screens. We're working on an update to allow the books to fill the new, taller, screen fully, with more text on every page.
It will take a little while. We don't want to release it until we can be sure it works really well on real iPhones. After we've got it ready, Apple always takes a little while to review new updates before releasing them in the App Store - typically at least a week or two. It's certainly coming though, and will hopefully be worth the wait.