Fluid vs fixed content area and "Size"

I have read somewhere that readability is optimized using about 55-60 characters per line for web content. Long sentences are difficult to read on screen, and long segments of characters tend to reduce comprehension.

That should also be the case for eBooks.

However, when starting out to design my first ever eBook, I find myself contemplating to use a 3-column CSS layout. The “holy grail” that is described (http://www.glish.com/css/7.asp) uses a fluid mid column in order to cover the full screen. I could use that approach, putting a cool NAV part in the left (fixed width) column, text in center (fluid) and whatever I can come up with in the right one.

But if I use a fluid center, where I’ll put my text content, readability may suffer greatly depending on screen resolution of the reader. I could of course set the width to a fixed size.

But then I would limit the usefulness of the “Size” tool included in the Active Ebook software.

?? Help!

What would you gurus suggest to get a good result?

Disable the “Size” button and force my preferences upon the reader in a fixed setting? Or go with a fluid setting and give the reader some freedom of choice?

Grateful for all and any feedback on this issue!

ALSO, I wonder - when designing for the web, browser compatibility is a big issue. Is that also the case for Activ Ebooks? It does rely on IE being installed, but does that mean that AEC also inherits the general **** ness of IE with regards to CSS interpretation etc?

You've hit upon one of my pet peeves. Where in the world does anyone come across a line of text that is 18" long--only on the Internet.