Ask HN: Who here (successfully) uses lead generation services?

Recently I discovered a few services that offer sales leads as a service. They seem to be able to put you in direct contact with exactly who you want to sell to. These guys [0] provide a massive database of companies and their respective representatives to contact. You can find the leads you want by using searches and filters on the business database. This other service [1] provides you with actual leads.

Does anyone have experience using these services for customer acquisition? Do they work (and for what kind of business)?

[0] http://www.afriseek.com/index.php (I'm based in South Africa)

[1] http://www.saquotes.co.za/join-saquotes.html?gclid=CJz_zvjTjLoCFbDMtAodSTgA3A