One of the best ways to drive people from your web site is to ask people to complete a long registration form before you let them download the whitepaper/software/information you’ve provided.
A rough rule of thumb is the greater the number of questions you ask, the greater the chance that someone will bail out and leave the form and probably the site.
Brian Carroll blog post Social media’s impact on web forms and landing pages makes a case for breaking down you conversions into a series of micro conversions.
On your initial registration form may not to want to ask for anything more than the email address. As someone returns to your web site, you can start to gently ask them for more information to build up a complete picture.