Ask HN: Any experience with a JS navigation help system to improve conversion?

We're looking for a callout / notification system that could be embedded in a webapp to help user navigate / understand the usage...<p>Questions: 1) Do you know any good product already designed for this purpose? 2) Do you have any experience in actually improving conversion rates?<p>I know that a good design could already improve the easiness of use.. but we would like to test a contextual help system.<p>Thanks!<p>M.