A quick tip: I really love the Kindle app for my Android phone. As a result, I have accumulated a fair number of books on my device. Unfortunately, the time it takes for the app to be 100% up and running after launching it–that is, for the book I’m currently reading to be open on the last page read–has also been increasing.
Fortunately, this is easy to fix: delete older books from your device. Don’t worry: Amazon will still keep track of what you bought, and indeed, in the latest version of the Kindle app, you can see them listed in the “Archive” section. You can re-download them whenever you wish.
With only a few (4/5) books on my Captivate, start-up time is back to what it was when I first downloaded the app. I think the root of the problem is that, for every book you have on your device, the Kindle app must sync your bookmarks and furthest location with the Amazon servers. If you have lots of books, this can take a while. The evidence seems consistent with this.
What’s not clear to me is why the app doesn’t instead only sync “on demand”: that is, whenever you open a particular book, it syncs with Amazon, but otherwise it does nothing. So, in particular, if you close the app while reading a book, then reopen it, only your current book will be synced. Perhaps in a future update…