Aru makes a great point, the OpticBook may be a bit of a unitasker, but it's brilliant for scanning books.
In preperation of getting my Sony Reader I went ahead and scanned one of my books. I used to do this when I had a tablet PC so I had some experience. Moving them from OCR'd PDF's to a text format was really where the hrad bit came in.
If you can afford to spend the money on the
OpticBook (a bit under 300 at Amazon, I believe) it is the single best investment you can make in this area - you can, as someone mentioned, scan very quickly and watch a movie at the same time.
The next part is the OCR. This is where it gets tricky, as most OCR programs will absolutely make a wreck of things. I would use greyscale here, btw... in my experience, it comes out better than black and white. Your mileage may vary.
Depending on your platform, you'll have a few options available to you. Most the free ones I've tried are crap. The one that comes with Adobe Acrobat is average, and the best I've used is OmniPage Pro (but hard to get a hold of for an individual, very expensive. Maybe your school or business has it.) Once you OCR it into text the laborous process is going through and cleaning it all up.
The book I made took me about 5 hrs all around, I'd say - but this was a test run, and so there were lots of false starts. I imagine it'd take me about 2-3 hrs now, for an average sized book, and I'd call it worth it.
I plan on writing a tutorial about this once I nail down some fine points. In the meantime, I suggest you look here - it's aimed at Tablet PC users, but there is an enormous amount of useful material here on the subject.
OpticBook Tutorial (other methods are mentioned as well on other pages here)