If the site where the form was filled out sets the users' collected info as rather obviously-named Javascript cookies or PHP session vars (i.e. $_SESSION[email]=$_POST[email]), that's one method, no?

Was anything mentioned about the browser used? Maybe when "auto-fill" browser options are enabled for a user there's a way to access that data.

The site does include their Javascript.

So I signed up for a demo account and installed (and hastily removed) the tracker

The article author signed up for a demo account after receiving the b2b marketing email containing "a report snapshot for 42Floors.com showing names, companies, and emails of site visitors and the information seemed plausible."

Like the parent, I have no idea how this information could have been obtained. It lists search terms, how could a 3rd party track clicks from SERPs to a website not running their tracking code?

Perhaps I'm being dense here, but the blog post says he signed up for the demo AFTER getting an email that included a "snapshot" of visitors.

The snapshot is fake:

http://news.ycombinator.com/item?id=4911542