I've never used a hyphen in the domain name, and I would actually steer clear of creating new EMD's. Too much info on the web telling people to use EMD's and everyone is doing it. I wouldn't worry about it. Pick a brand thats catchy, people will remember it more.
The major problem that occurs while using a hyphen in domain name that is at the time of marketing your domain name by word of mouth because it is difficult to remember a domain name with hyphen. Apart from this there is no problem for using a hyphen in domain name.
Domain name represents your brand. So for branding purpose, you should never use a hyphen in a domain name. But if you are just thinking to take a domain name and after that you are doing SEO, there is nothing harmful..
From a SEO perspective it makes no difference... G does not prefer one over the other... However my preference is without the hypthen as people tend to remember URLs better.... Also if a website is not available without hyphen and you choose to go for the hyphened name - then I am sure that this could cause problems too with regards to branding, copyright etc... So I would also stay away from that too.... In some cases it makes sense to buy the two versions and redirect one to the other if you are serious about protecting your brand....