How to retrieve custom user registration data back into a form?

The merge tag for outputting user meta is currently undocumented. You are on the right track, however you need to make sure your key is correct and that means case sensitive also.

This is the merge tag for displaying user meta:

{user:key}

So if you create custom user meta using the User Registration Add-On and name the custom field companyname you would return the value in a field by using this in the Default Value for that field:

{user:companyname}

I just verified that this works in the latest release of Gravity Forms. I created a brand new form and populated it with that merge tag. I then created a registration form and used the User Registration Add-On to configure a field that creates custom user meta using the key companyname.

I then submitted the form and created a new user, logged in and browsed the form I created using that merge tag as a default value. It populated the field with my custom user meta value.

So that merge tag does work, but you must make sure that the key you pass is indeed 100% correct.

We don't have a video tutorial for this.

Here is a screenshot of a text field configured to set the default value equal to a custom user meta field with the key name company: http://i.imgur.com/EBoAK.png

With the field configured like that the default value would be populated with the value of a custom user meta field with the name company. This is just an example, of you don't have a custom user meta using company as it's name it obviously wouldn't work.