You can start taking notes without setting up an account, but with an account you'll be able to access your notes across multiple devices (including your computer). You can save, share, and print your notes, as well as have them emailed to your Kindle.Also, the app will save your notes automatically once a minute.
One (small) downside, though, is that this app is fixated on bullet points. You can't type up several paragraphs of notes without having a bullet point assigned to each paragraph. It's a small thing, and it doesn't bother me any. But one slightly more important bug is that when you're typing from the Kindle and the app saves your notes, the cursor is moved back to the beginning of the text field.