There are a few of these threads been started, and from them I have gleamed the following:
1) Old school do not like hyphens (its not the way they made their money)
2) It is often quoted that hyphenated names will lose traffic to unhyphenated names (only 15% of traffic is type-in, the remaining 85% is search engine)
3) If a domain name, in say .com, is valued at $50,000 there is a chance the hyphenated is unregistered and could still be worth $5,000 for an $8 investment.
4) A good developed site will not lose much traffic (as in 2 above) because people bookmark sites they intend to return to
5) Search engines prefer hyphenated domains (hyphens between words)
6) The owner of a developed site with an unhyphenated name would be well advised to purchase the hyphenated name to protect his/her market share
7) Hyphenated multiple word domain names are 'better' at being recognised at first glance and more memorable via sight than unhyphenated multi-word domains
8) Many domain names are automatically barred from many user protection programs because of the 'letter string' involved, i.e. Penisland.com because it contains the string 'penis', whereas the hyphenated Pen-Island.com is not barred.
Just a few points.