I like hyphens because they are easier to read. I also read somewhere that with hyphens, the big G has a better idea of what your keywords are. (Assuming you have keywords in your domain name.) One of my domains has a hyphen and I don't see that it is penalized at all for it.
Side note: My 200th post and it isn't even the spammy one I was planning on.
Only 800 to go!
