This hint facilitates right-sizing text documents so that you can save them as PDFs for easy viewing on iPhone, typically in Stanza or some other reader app. I haven't used it on iPad, since the screen is large enough that the special preparation is not usually necessary. It has not been tested in iBooks, but I think it would work well there.
It's probably most useful with small text documents, not book-sized docs or images. I used it to create a list of requirements and prices for use while selecting a pay-per-use-cell phone at the store.
The key is to make the text narrow enough that it is readable on the iPhone without requiring continual horizontal scrolling. A downside is that the PDF will probably be unreadable on iPhone until you zoom in on it some.
Prepare your text in TextEdit or some other word processor that has the concept of a page width; I'll describe the process for TextEdit in 10.6.7 (probably the same for all 10.6 versions).
Once it's ready, select File » Page Setup, and in the Paper Size menu select Manage Custom Sizes.
In the resulting dialog, click the '+' near the lower left to add a custom paper size.
In the Paper Size field at upper right, set a narrow width (I used 15 cm, about 5.9 inches). Set Height as you wish, or leave it unchanged. The width is the important setting.
Below that, ignore Non-Printable Area, and move on to set the margins so:
Mac OS X Hints
http://hints.macworld.com/article.php?story=2011051600392766