Or how about when you start reading and the words run together in places or disappear into the binding?
No matter how great your writing is, a cheap feel or terrible layout can be the death of a good book. This is why it is very important to have an understanding of book formatting, even if you are not doing it yourself. There are bounds of tutorials across the net that will help you garner a working understanding of this process, as well as explaining paper types and guidelines in explicit detail.
Formatting is like your business card. Regardless of who does your formatting - a publisher, a freelance book designer, or you - the only thing a reader associates your book with is YOU, the author. Your book's formatting and feel will determine how a reader sees your work - whether as legitimate or as one of those amateur self-published books that have earned such a nasty reputation over the years. Remember, while you may not consider yourself in the same league as Stephen King, JK Rowling, and James Patterson - the reader lumps you all together. If they have to bend the spine backwards to read words that trail off into the bindings... well, it's likely that they won't read much further and will return to one of the larger known authors with professional formatting.
What a lot of authors don't realize is that they need to spend as much effort on the formatting as they do on the writing for the book to have any shot at being a success. If you're doing it yourself - invest the time and money into a layout software like Adobe InDesign. This professional style software will allow you to tweak settings that are unavailable to you in a word processor. If you're not computer savvy, it is best to hire a professional. There are plenty of experienced book designers available all across the internet. You're bound to be able to find someone to fit your budget. If you're being published by a legitimate publishing house - chances are they have professionals using software such as InDesign and will handle it for you - but make sure that you get final approval and peruse your sample copy with a fine toothed comb to ensure no detail is missed. Your book depends on it.
While we are all told "Not to judge a book by its cover" while growing up - as an author, you need to face facts. We all do it. We're all guilty of it. And your book will not be treated any differently. You've seen how people select books while browsing bookshops - they pick them up, turn them from front to back, inspecting the covers before flipping through a handful of pages. If your book does not meet or exceed the industry standards - it will go right back onto the shelf. And your royalties go with it.
Make sure your book doesn't meet the same fate... Focus on your formatting.