Has anyone set-up their website available content so that with only one form fill-out a lead can download multiple pieces of content?

When you set up a form you have the ability to show custom HTML if it is a returning visitor, this includes things such as Welcome Back, Cotter! 

So they don;t have to refill in the form the second time.  This is found on the setting tab of the edit form screen.

Colette, to wrap up Jamie and Josh's answers, which are both correct but may seem contradictory...

When you use the Known Lead HTML feature, if a lead has previously filled out the form in the browser, custom HTML is displayed. 

By default, this HTML includes the form submit button, labeled as Download, which when pressed will take the user to the form's Thank You URL (or call the custom onSuccess JS function, if you're using one).  In this default case, as Josh points out, an additional form fill is registered in the lead's activity log.

However, the custom HTML does not have to contain a submit button. It could be modified so it only contains direct download links.  In this case, the links will (by default) be registered as Clicked Link in Web Page activities on the lead, but there won't be a form fill.

So when you speak of allowing "any and all the content" you could deliver using either method.

I've done something like you're requesting, but it's very custom and I'm working on making it far more dynamic.

Here's what happens: In my programs, I have a token for "Allow Form Bypass If Known" which you set to true or false.  This does what it sounds like.

I then have a cookie for two different forms: Known and Unknown.  When I create a form I change the name to include the Form ID number, so a form could be "Contact Us - Known - 1234" or "Contact Us - Unknown - 2345".

I also have a cookie for "Form Bypass Days"

In my landing page template I have a function that checks to see if the visitor is currently cookied as having filled out a form for that product.  If they are, I skip the form and instead put in a button to take them to the asset.

If they don't have a current cookie but are a known lead, they're presented with the appropriate form which excludes demographic information like name, email, address, phone, etc.

When they fill out the form I set a cookie on their browser for that product, for the "Form Bypass Days" amount of days which, if set to 10, would mean that they don't fill out another form for 10 days.

Now, what I'm working on is picking out the right questions to ask.  So let's say I have a form for "Budget Questions" or "timeframe Questions".  Here's how this works: I ask you Timeframe to Purchase, you say "3-6 months".  I will now set a Timeframe question with 90 bypass days so you won't get asked Timeframe again for 3 months. 

For Budget, let's say I know budgets typically are set in January or July.  If you've answered a question on budget since January but before July, I don't ask budget again.

So the next time you're eligible to fill out a form I'll check to see which forms you're currently cookied as having set and loop through until I find the next priority of questions.

This is like progressive profiling, except it solves a big problem of progressive profiling: resetting certain data fields. Once a PP question is filled out, it doesn't get asked again until it's erased (and I don't know a good way to null out fields). But this gives you more control.

The downside is that it requires significant javascripting. FWIW, I barely know anything about JS and was able to write up all the needed code by simply googling what I want to do and finding examples on the web.

Now, to take things to the next level....

For my Nurture Marketing program, I use one single landing page for 4 different content pages.  I have a token called "Gated Assets" where I set which pieces I want a form to display.  With this, I enter "autodemo, case-study" in the token and then my link to the page is page.com?asset=autodemo and it will put up a form.  If I put page.com?asset=brochure it doesn't show a form BUT I can still track it as a click / form fill.