Google tends to give weight to keywords in the domain name. This increases the importance of selecting a good name.
When choosing a domain name for SEO purposes, there are three main factors to consider:
• Brand
• Rankability
• Linkability
Brand
Should you use hyphenated, multi-term domain like search-engine-marketing -services.com?
I'd avoid such names like the plague.
Why?
They have no branding value. They have limited SEO value. Even if you do manage to get such a domain top ten, you're probably going to need to sell on the first visit, as few people are going to remember it once they leave. It is too generic, and it lacks credibility.
In a crowded market, brand offers a point of distinction.
It is easier to build links to branded domain names. People take these name more seriously that keyword-keyword-keyword-keyword.com, which looks spammy and isn't fooling anyone. Would you link to such a name? By doing so, it devalues your own content .
It can even difficult to get such domain names linked to when you pay for the privilege! Directory editors often reject these names on sight, because such names are often associated with low-quality content. Imagine how many free links you might be losing by choosing such a name.
Is there a downside to using branded names?
Yes.
Unless you have a huge marketing budget, no one is going to search for perseefgxcbtrfy.com, which is a new killer, brand I just made up ;)
Thankfully, there is a happy medium between brand and SEO strategy.

Rankability
SEOs release the value of keywords. When naming your site, and deciding on a domain name, try combining the lessons of SEO, branding and domaining.
Genric + term is a good approach to use. Take your chosen keyword, and simply add another word on the end. SeoBook, Travelocity, FlightsCity, CarHub, bydomain.webs.com , etc. These words have SEO value built into them, because people are forced to use your keywords in the link. Also, Google (currently) values a keyword within the domain name for ranking purposes. Finally, such a name retains an element of unique branding. These types of domain names score high on the rank-ability and link-ability meter. They are generic enough to rank well for the keyword term, yet contain just enough branding difference to be memorable.
The SEO Advantage
There is another advantage for SEOs in the domain space.
Dot com's can sell for 5-20 times as much as a .org or .net. Keyword + .com can sell for millions of dollars, depending on the domain name.
Expensive, huh.
But...
By registering or buying the cheaper .net or .org equivalent, building out the site, and ranking well for the keyword + net, or +org, you increase the value of the domain name markedly. Sure, you're one step away from pure domaineering and you still have Google to contend with, but you'll be head and shoulders above those who are undervaluing these names. A lot of domaineers aren't operating in this space. Yet.
Other Tips And Ideas
Leave The Keyword Out Entirely
Used the related search function on Google ~ + keyword and see if any of the related keyword terms fit. This can be a good strategy to use if all the good generic keyword names are gone. It might get you close enough to the action, without the enormous price tag. Might be more memorable, too.
How To Test A Domain Name For Penalties Before Buying It
• Verify the site is not blocking GoogleBot in their robots.txt file
• Point a link at the domain from a trusted site and see if Google indexes it
• Within a couple weeks (at most a month) Google should list the site when you search for it in Google using site:domainname.com