I think this book is indispensable, and it's definitely one to buy rather than borrow. I've read it cover to cover a few times, and I still learn something new from it each time (as my skill slowly improves); I also keep it close to hand so that I can refer to specific sections.
Chapter 5 is worth the purchase price by itself; even though the book is 11 years old, and there have been several new software releases since then, I still had to jump through the hoops before the computer colours would work correctly. Without that, I got a weird effect (in Photoshop CC 2014) where my drawings almost looked like a photo negative.
Personally, I found the colouring section more useful than the lettering section. Todd Klein covers three topics: hand lettering, creating your own font, and computer lettering with an existing font. Computer lettering is the only part that's relevant to me at the moment, but the rest of it may come in handy at some point; if nothing else, I now appreciate how much work is involved in creating a good font!
There were a few typos in the lettering section (e.g. "your" vs "you're", and "percemt"). That surprised me, because I'd expect someone who letters by hand to have impeccable spelling! However, these mistakes didn't detract from the points he was making.