Actually all of the lead generation services work. Unfortuneately, many are matched to a task for which the service can not succeed. (i.e. selling homes in the newpaper)
Identifying the service best sutited for your business model requires a few questions.
#1. Are you exclusively looking for the 90 day market?
#2. Are you equipped to incubate a lead for 18, 24, 36 months?
#3. How do you want the consumer to respond?
#4. What do you have to offer to get the consumer to respond as desired?
Example: You are able to offer "if I don't sell your home in 60 days I buy it myself!" (hey, it's an extreme example!) Do you think you actually need a lead company to get names and numbers with that offer? This you can do yourself!
Real estate business is rich with propositions to the consumer. Define your proposition, write great copy, and use the many free resources available to create your lead generating system. If you don't have the time to generate your own leads, you need to look at the 800 pound gorilla. Realtor.com.