To my knowledge readers of an eBook have to use the viewer created by the eBook -- although I've heard Adobe has a separate eBook viewer, but not sure why anyone would want it if they already have the Acrobat Reader installed.
Personally, I like the Microsoft Reader. The "clear-type" makes text easy to read, and it's easy to search pages, bookmark pages, and maintains it's own library. By the way, their definition of the "clear-type" is:
"ClearType that enhances display resolution by as much as 300 percent by improving letter shapes and character spacing, making them appear more detailed, more finely crafted, and more like printed fonts."
Publishing in ".lit" format is a snap. There is a program you can download that runs as a macro under the file menu in Word. You just click the menu icon and it's done.
The Microsoft Reader doesn't seem to be very popular though. It is rare that I stumble across anyone publishing in this format. I was publishing my newsletter in both PDF and LIT format over a year ago, and 95% of the downloads for the newsletter were in PDF.