I went on Backpages a few weeks ago, and it did definitely bring some leads, but I agree with LL that they weren't desirable ones (like you I only see white clients, and that ad seemed to draw a lot of men from other ethnicities - who were also incapable of reading...). I edited it to include the URL to my website (which didn't seem to be an option when doing the ad), but I'm not sure it made much difference.
I'm going to try VivaStreet, though I wasn't too impressed at first glance.