The rule of thumb in advertising is, a prospect needs seven exposures before they will take any kind of action. This holds true for the Internet. Either your site must be so compelling, that they keep coming back. Or you need to gather their contact info, so that you can continue to bring your marketing message to them again and again. Don't simply ask prospects for their contact information.
People are very wary of handing out personal information.
They want to know what's in it for them, before they'll give you such valuable information. Once you have their e-mail address, immediately contact the prospect. Immediately send your prospect information about the benefits of doing business with you. This allows you to send special announcements, tips, industry information, etc. You can even set the listserver to send a final batch of information if a prospect asks to be unsubscribed from your list.