I've been banging out tiny niche sites and the ONLY ones that haven't ranked are the ones that I used dashes in the domain. I think there's two aspects to this.
If you want to rank IMMEDIATELY in a tiny niche, then avoid dashes. If you want to build an authority site, then it's irrelevant. With enough back links you can rank any domain for any keyword.
I've got a little formula going where I use the same template, go after (roughly) the same amount of searches and the same amount of competition. When they get indexed, I can place my sites in the top 3 pages, then with a couple of ezine article links I end up on page one. (Like I said, they're small niches) The ONLY things that don't work for me are dashes and .infos. This whole process usually takes 3-5 weeks. If someone loves dashes, please state how fast you ranked and how many back links did you push?