I think SEObook.com is a stronger brand name than
seo-book.com
it is going to depend from domain to domain and how good you are at branding and where you intend to get your traffic from (search engines or other sites, etc)
there is no clear cut answer in my opinion. I think it is possible to get your keywords in the domain name without using dashes, but some people prefer dashes because some people do link to sites using
http://www.seobook.com
usually most people link to me using "SEO Book" as the text though, but some do use seobook.com as the text.