Just read an interesting free report called "Death of the Salesletter" by Michael Fortin.
He points out that sales letters are evolving - at least the good ones are (forcing the bad ones to simply drop out of existence).
Opt-in forms used to be enough. Then they added ethical bribes on an if-then basis (click on this link and then I'll give you a goodie...).
With the rise in interactivity, it looks that you have to give samples of the goods in advance, as well as the bonuses.
This gives you a problem, as you simply can't be bothered with the expense of that bandwidth for the bonuses. However, you can offer several different bonuses, one of which can be selected by the reader for their participation. A drop-down form, which then triggers an event when all the points are filled out. (One idea could be to give them the option of bonuses by showing a tool-tip type of popup which shows the cover of that ebook as a small graphic... while not giving the download away to begin with.)
Also means you want to have pop-ups which show when the buyer wants more data. Images should open in another window for a larger view. Of course, this means a great deal more homework and making sure your sales page works in different browsers.
What you're doing is increasing interactivity and letting the reader participate in your page more. You are letting the person sell herself in the way she wants to be sold. Want more data, click here. Want more pictures, click here. Sample of this stuff - download this link.
Probably means building several pages of data into one. Such that the page actually builds depending on what the person wants to see. Tricky, but probably worth it - if it can be kept on a single page without having to access data from a server (client side).
Solves the problem of the overlong sales letter (I will often page down to see what price they are charging rather than read all the gorgeous testimonials and bonuses). You would click on testimonials, or guarantees, or whatever you want and then the page would change to reflect that request.
Mouseovers look to be one item - with tool tips that explain something. However, these would need to be linked to an obvious mouseover, so that the person isn't annoyed by surprises.
Ideally, you'd have inline CSS - a longer page load, but you aren't then missing a needed file when it has to pull up two to get one result.
Right now, I'm looking at tool tips and splash screens which are viewer oriented - not those annoying pop-ups, dynamic or otherwise. What I would really like is a collapsible page - one which would fold down when you wanted more data, and fold up to get out of the way.
The whole concept is to keep them on that page, but make it as interactive as possible. You'd have all the points of the sales page, but then hide the ones they didn't want to see. Like overlong testimonials - or more about the guarantee - or price options (whew - now that would be interesting, set your own price...)
In our case, we are simply wanting the person to opt-in to recieve the newsletter, but have an incredible amount of data to share (which is why the newsletter).
To start with, we simply give the first issue out as a sample - downloadable PDF, plus a pop-up graphic of what the first page looks like. The graphic of the product box would pop-up larger. Each section would be a simple link (more|less data) which would expand that section or contract it. In my case, I'd probably stick to pop-ups - like, "Who is this guy, anyway?"
Obviously, this is subject to testing. I can only work from what I like and what I expect out of a page.
But the idea of a highly interactive web page is always an exciting one.