Many books are not properly proof-read and edited after the OCR process.  Some of them include things like the book or chapter title in the text itself, once for each time it appears on a page.  Many books have spelling mistakes, especially for books which feature odd or made-up words.
There are a zillion zillion e-book formats and the book you’ve just downloaded is not in the one you want.  You have to somehow convert it to the format your (pre-kindle) reader supports.

Now that the kindle and iPad are creating their own captive e-book markets, with certain specified formats, you will see the pirate e-books adopt those formats and they will become de-facto standards (if they haven’t already, I admit I’m not familiar with the formats they use).  Once the format is standard it will be as easy for an iPad or a kindle user to download a book and put it on his or her device and use it (unless the device locks out unrecognized/unauthorized content? It’s possible).
Personally, I wish I could buy the paper book and pay a small fee ($2-$5) to receive an unrestricted electronic copy as well.  But considering a paperback novel costs in the range of $10-$15 I can’t imagine paying $10 for an electronic book that is locked to a specific device, which I can’t share or back-up appropriately.