The thing with hyphens is not the hyphens itself, but the use and amount of hyphens in the domain name. If there are two many hyphens in the domain name Google won't value your site as highly, is what some people say. This is what I've read from many sources on internet, googling, and e-books and junk. Other people say hyphens don't matter and that it is even beneficial for your domain to have hyphens to distinguish keywords.
Instead, I find it better to look at Google myself and look at where hyphenated domains tend to rank. What I found is that there are indeed heavily hyphenated domains ranking for many #1 keywords. I didn't really go in-depth, just used MS, and saw that these keywords did have some pretty decent competition, with sites having decent 2+ PR and domain ages of 1+ and decent BLP 1000+.
I didn't really see that hyphenated domain names had to work twice hard with backlinks or something as some people claim. Instead what I found was that both hyphenated and non-hyphenated domains always tend to rank with far less backlinks IF the rest of the competition does not have the keyword phrase in the domain name.
I don't know but I tend to care less about whether to hyphenate domain names than looking for the keyword I want to rank for in the domain name itself. What bugs is me when the competition is so fierce that you can't even buy hyphenated domain names. It actually happens to me all the time so I'm glad if I can even get hyphenate domain names sometimes.