Hey Chris, do both and test.
It's been a couple of years, but I tested a couple of two-word domain pairs for which I own the hyphenated and non-hyphenated versions. The non-hyphenated got more type-ins, but the hyphenated got (much) better search rankings.
I wouldn't hyphenate more than three words, however, to avoid a penalty, i.e. keyword spammed names like
www.free-teen-cheerleader-porno-videos.com are right out.
Hope this helps
