Looking over many companies' marketing initiatives, there are definitely items for which people are prepared to give up their contact details, and ones for which they are not.
Last week in Do you need your prospect's contact information?, I touched on the old argument about whether you should give your content away (and ensure the widest possible distribution), or if you should ask for contact details in return (getting you prospect names and addresses). There's no right and wrong way, of course, but looking over many companies' marketing initiatives, there are definitely items for which people are prepared to give up their contact details, and ones for which they are not. The difference? The value of the item to them.
Now, before you say "that's obvious", think about it a little harder. Imagine that in asking someone to give up their contact details, you're asking for a payment. It's a fair, and very revealing, exercise. Now look again at any material which you could make available for free download, but instead are asking "payment" for.
Do you seriously think that "a list of reasons why we're a great supplier" or even a data sheet, would generate significant income if you put a cover price on it? No, of course it wouldn't. Imagine having a pile of them at an exhibition, and trying to sell them to visitors. On the other hand, an authoritative guide to your technology? Now, that might easily persuade people to dip their hand in their pocket.
I'm not suggesting that your marketing plan must include the production of genuinely useful publications (although it's working well for many companies). But if your content is clearly aimed at selling your product, don't expect prospects to put in any effort to obtain it. "Fill in this form to download the document" simply won't work if you're the one who's seen to be getting the benefit, not the prospect. Just get the document distributed to as many people as possible.