There have been many discussions about this: http://www.google.com/search?hl=en&...+site:www.highrankings.com&btnG=Google+Search
Hyphen is a good seperator of keywords. I would prefer a domain with one hyphen seperating the keywords then without the hyphen.
yes i would also go for domain with hypen and keywords if i have to register a new domain for site. hypen is treated as join while and it is more readable to visitors
SERPs are Search Engine Result Pages in which the search engines rank the closeness of the result from the typed keyword. The key to good rankings in Search Engines are Keywords and the content.