I ran into some bugs using the new online editor that I had to work around today, and I figured I'd relay what happened in case someone else has the same problem.
Problem 1. I published a book last night, but took it off sale today because the internal cover image was cut-off when I viewed it on both the phone app and on my nook color.
The Problem: I had used the "Add front matter" button to automatically create an internal cover image. The problem is that it inserts the cover at the same resolution used for the website. Since nook requires 1400+ pixels for the website image, it will be too big to display on any device.
The Workaround: Don't use the "Add front matter" cover section. Just delete the chapter. If you want an internal cover image you can create a regular chapter and insert a copy of the cover at a smaller resolution.
Problem 2. After I took the book off sale, I couldn't make any edits to the manuscript.
The Problem: You can't make edits to a file after it has been published. You can change the cover image, Nook Book details (title and description, categories, rights and pricing, other information) and you can add reviews, but you cannot change the actual file. I'm not sure if this is a bug or just a fact, but I didn't realize this.
The Workaround: Download the epub file and upload it again as a new project.
Feel free to chime in with any better solutions to these problems, or let me know if I'm the only one having these issues.