Cari Jensen did some experimenting with the new image export features of EPUB in InDesign CS5.5. Maybe you'll find it helpful:
[Edit:] Oops. Just noticed you read Cari's post. She's explored this more than anyone else I know.
You might also look at Liz Castro's blog:
Thanks for your reply Steve. I have Liz's book. I was typing some more info when your reply came in - I have just found on her blog that iBooks has a bug that means it ignores size attributes on the img tag. Knowing that I could now apply the sizing instructions to the containing div the images are in - they are in consecutive paragraphs which float each other, so they line up horizontally. Having a play with that I think this means I can't get the paras to float and be sized by the containing div.
I hate iBooks!
If I tell the containing div to be a certain height my float doesn't work. If I tell the div to be a certain width it works in iBooks but then Adobe Digital Editions looks wrong (images stretched to the full width of the page, but at the specified height).
I think I need to get my Indesign export to have the images at the correct size (like in effect what CS5 did when "Formatted" was selected). I tried a script (by Kasyan Servetsky) which made all the images 100% but it didn't work quite as expected - the image files were resized but I had to go through the document changing their scaling to 100%. Does anyone know of an easy method to achieve this? If not I'll have to unzip the ePub and check/adjust all the image files to make sure they are consistently sized.
Forget ADE. It's way too out of date for testing epubs. It's in serious need of an update.
I know Bob - but the guy assessing and ultimately paying for the files uses ADE! And I know several hardware devices use the ADE engine. I think we'll have to say something like "Best viewed on ...". I have already warned him about how they will look different on different devices but I'll have to reemphasise that.
I wish we could skip forward 2 years when this has all shaken out and the market tools/devices/expectations were a lot more aligned!
Don't count on it. This is the same problem with websites and different browsers.
The benefit for epub is that you can actually create different files for different devices before submitting them to Amazon, iTunes, etc.