there have been many discussions here about keywords and domain names (have a search you will find some great discussions).
one thing i have noticed (lately) is that google can pick a word out of a domain regardless of whether there is a hyphen or not.
using a hyphen can get better results with inbound link text as people will tend to separate your keywords (domain name) instead of lumping it all together.
personally, i get both :)
dazz