I have to disagree Chris.
I was at a panel discussion at the NAR mid-year meetings recently and Sami Inkinen, Trulia's Chief Operating Officer was a participant. He said Trulia was mostly a marketing company more closely akin to Zillow than Realtor.com.
Here's a blog I wrote about the panel. Very nice blog, there are a lot of good points. I agree with what you are saying in general. My thoughts on the matter are that as knowledge of these nationwide sites becomes more and more prevalent, I believe that buyers will more than likely be heading to the Realtor.com and Trulia.com sites first and foremost rather than a Google search for "Salina KS Real Estate".
For example, let's say a potential buyer is searching for a 4 bedroom home priced between $300,000 and $350,000. If I happen to have a current, active listing and I'm on HAR.com, Trulia.com or any of the others I MAY have a chance of getting contacted for that one home.
But on my website, via my IDX link, I always have a large selection of 4 bedroom homes priced between $300,000 to $350,000 and since I'm also the only Realtor that appears on my website, if they contact anyone about that listing it's gonna be me.
NAR statistics show that over 70% of buyers & sellers do business with the first Realtor they contact.
My thought is that if I can't for what ever reason get them to my site directly, I sure want to at least make sure that my properties are on the nationwide MLS for the chance to be the buyers agent or at least be able to sell my sellers property to whom ever ends up as that particular buyers agent.
I see the national MLS's as an extension of my advertising campaign to sell properties. I don't see them being nearly as beneficial to to a local customer looking to buy elsewhere since, as mentioned above, real estate sales are still a primarily local business.
I will admit that I am a bit biased as our company was born out of and continues to thrive from nationwide (and worldwide) advertising as our base of sales. We sell approximately 70-80% of our properties to people out of the area, state or in some cases out of the country.
Thanks,
Chris