It is very true keywords in domain names are very important.
When choosing a new domain, two directions can be taken : either create a new term, that does not exist, like a brand, or to use interesting keywords if possible.
The idea behind it is the domain name will weight a lot in search results.
If you go for "new brand" (like -www.hihohiha.com) you'll be most likely first on the "hihohiha" search query with not much efforts (as it's a new term) and this is quite à good thing. But you'll have to work more to associate other keywords to your site.
If you're lucky enough to be able to choose a domain with one or two real good keywords (here good means searched for a lot), it will be easier to obtain good results with those, cons are very few, but you need your domain name to be user friendly as well, so it could be harder this way to build up a clear identity for your web site (that's why brand exists
), especially if you're the challenger and not the leader on those keywords.
To make it short, keyword in domain name should, IMHO, not restrict your web site topic too much, because you could have to work hard to tell this site is not only about this or this.
For example this site is using two keywords really matching topics covered here : "phpBB" and "SEO", and this help out
but does not do all