Update the app and you'll find that the TOC for some ebooks has been moved into the left menu panel (from wherever it was inside the ebook), and that the X-Ray feature has been integrated into the search function.
The TOC tweak is going to make it easier to navigate; the Kindle iOS app lacks a back button so simply looking at the TOC before meant I lost my place in the ebook. And thanks to the changes to the X-Ray feature, it's now as accessible as looking up a term in the dictionary, Wikipedia, or Google. This will be nice should I ever pick up the next volume of Game of Thrones series (not likely).
You can find the app in iTunes.
Update: I'm wrong in saying that the app lacks a back button; there is a button but apparently I can't get it to work reliably.