At present that's all it supports. InDesign supports both but it's expensive verses free. Even with InDesign at present you need to do seperate layouts for each orientation. There's an InDesign upgrade that supports text flow in May so you can do one layout for every device and orientation.
I hope Apple adds Portrait support eventually but it could be a year or more so I wouldn't hold my breath. Right now it just crams your content to the left and the text to the right. An ugly option. I'd rather have it lock in landscape personally. I'm guessing they had to pick one so they could rush out Author. I'm guessing they went with Landscape because their big push is text books and it's more attractive for content with lots of images.
Wish I had better news but it's all in it's infancy.
There's simply no way to make it look good in portrait in the current version. Essentially it defaults to a two column layout with art on one side and text on the other. The next edition of InDesign will address this issue but like I said it's expensive and not exactly drag and drop. Formatting can be a real headache with InDesign.
With Author make it look good in Landscape since it's the default layout then accept the fact portrait is just for people that want to read the text in that orientation. Personally I'd rather either be able to lock it as I said or have it drop all artwork in portrait than deal with a messy layout.
It's the early days and all this will go away over the next few years. I still remember thinking what a miracle the early spell checkers were back in the day.
There's simply no way to make it look good in portrait in the current version.
I agree the tool has limits, but I'm not sure I'd go that far, sorry
As for locking...
Personally I'd rather either be able to [clip]As always, feel free to use the 'Provide iBooks Author Feedback' menu item for features you'd like added in the future, etc.
http://www.apple.com/feedback/ibooks-author.html - also, you may want to start your own thread on what you'd like to see, so that it can receive the unique attention it deserves, etc.
Apologies, Giglic, for side tracking the thread
OK. I did eventually find it at the beginning of the sample document but it was greyed out. I've decided that it defeats the advantages of the iPad to compose for both portrait and landscape. Beside the effort, I'll wind up compromising the quality of the document to the least common denominator for portrait. So in the inspector Doc setting, I set "disable portrait display." Just like a printed book, it looks best the way the author laid it out. I'm sure Steve would agree that this feature can't be applied to every situation if it compromises the artistic integrity of the piece.