It depends on what you're using the dash for I've used a dash in one of my sites to rank for 2 phrases, and I still ranks number one for both the 2 terms I wanted For instance, I have the words {x, y, z} and I wanted to rank well for the phrases "x z" and "y z" My site is called x-yz.com, and I still seem to do well [obviously the name of the site isn't actually x-yz.com] However, I have noticed more attention is place on the earlier words (x) rather the later the later words z. It's worth bearing that in mind Edit.... you go to all the trouble to respond, and they want their question deleted! <sigh>
Domains with dashes may or may not rank better than domains without them, but from a resell standpoint domains without dashes will always be a premium and sell for more. Travis
Personally, I am a fan of using domain names without dashes in them. I agree with the above point about resell value, but in addition I think if you are going to keep the site for an extended period of time, then no dashes looks more professional.