Well, since I got my BeBook, I have been trying to find a perfect format for my books I have created and from others sources. I have come to conclusion that a PDF formatted specifically for 6" display is the best for my BeBook as what you see on the software you create PDF with is what you get on BeBook. No funny formattings and problems.
This is why I started to convert lots of text content from websites as well as from other formats and use this little converter application I have made that generates 9x12cm PDF document with enough big font to be nicely read on these 6" displays.
http://www.majgaj.com/txt2pdf
All you have to do is select some settings and paste text onto the editor box. The application reflows the text automatically so you don't have to worry about that, creates a title page if you wish and you can also set a delimeter where you want to have automatic chapters created.
I would like to hear some comments about txt2pdf as well.