Why does this work? Because at it’s core, list building is about trust. No trust, no signups.
Consider this test from WhichTestWon.com:
Be careful with what you say in your mini privacy statement
It is also possible to REDUCE your opt-in rate by adding an anti-spa statement, as this next test shows:
Also consider this excellent post on the series of tests that ContentVerve did with several privacy policies. Here’s the summary of results