With internet based marketing you generally don’t want to ask for too much information on a webform. One common practice is to take the minimum amount of information on the form and use a ‘data appending’ service e.g. Jigsaw, InsideView or LinkedIn to build out the details for a new lead e.g address and company information.
A quick and dirty, but effective technique is to send an email to your lead database on a public holiday – a high percentage of people have their Outlook ‘Out of Office’ switched on, which means you get a return email, often with a lot of useful detailed information, e.g. job title, direct phone number that can be used to append the lead record in your CRM system.