goodroi - 10:09 pm on Nov 10, 2011 (gmt 0)

IMHO website structure is much less important for SEO reasons. The search engines are looking at so many different quality signals that url structure often does not make a significant impact to your ranking score.

I would be much more concerned about building a url structure that #1 - will be easy to maintain in the long term and #2 - will help branding and usability efforts. A very long url with special characters makes it less likely for a user to pass it along to their friends.

ps hypens have been abused by spammers for so many years that I would suggest you be overly cautious and avoid them as much as possible