Welcome to Trulia - I see that you joined today!
I think it is safe to say that no one website or marketing technique will sell any one home. Trulia is certainly popular among consumers and I am talking to more and more clients each day who are familiar with Trulia and using it themselves to supplement our home search or to investigate areas.
I'm sure that Trulia has helped buyers find homes and sellers reach out to a broader base of clients or people relocating, but I doubt there are any statistics available on such sales.
Best of luck to you!!
1) Volume - Trulia was a top 3 referrer to 12 of our largest broker partner Web sites, according to Hitwise data from this Fall: http://www.truliablog.com/?p=207
2) Quality - The Trulia user is a highly attractive audience of serious home searchers - take a look at my blog post with results from our recent Trulia user survey: http://www.truliablog.com/?p=216
3) Measure by Others' successes - there is a great case study no Prudential Fox & Roach reporting that Trulia users were clicking to their site and requesting double the average # of showings than other user: http://images.trulia.com/resources/Trulia_Prudential_Fox_And
And if you purchase a monthly subscription to Agent Featured Listings you get: contact info displayed, ability for clients to email you direct, listings placed in the top 3 search results and weekly reporting you can forward to your clients. Plus, agents receive 4x the normal Trulia traffic on average through this product! http://www.trulia.com/agents/feature
Hope that helps.
Most Realtors track where the buyers for their listings have come from; however, I do not believe that Trulia has the means...or any website for that matter. Even our listing services do not ask us how the buyer found the home.