I am glad you are starting this trail Dave; this is actually a very genuine question for all of us part time webmasters.
Login as an Admin on your site, you should have access to Statistics and Site Reports. Two metrics to be watched on a weekly basis are "Daily Unique Visitors" and "Referrers".
"Referrers" allow you to see exactly from which domain or even better from which URL your visitors are coming from.
This is crucial as now one can make a sound business decision in term of advertizing dollars.
I have started to use Trulia extensively this month (Trulia Pro, Featured listings, Spotlight, posting blogs, answering more questions...). I have used Trulia for a few months prior mostly for listings advertizing.
For the month of September, I am averaging five (5) hits/day coming from Truliaâ€™s URLs.
If I can double/triple this number, I might stick with Trulia Pro and pay the monthly fee. I love Trulia and want to make it work so I will give it more time.
Again, great question. I really hope we have other folks jumping in and sharing their metrics/insights