How to use the userProfileLookup function

Hello,

I have a calculated value control that I'm trying to use to display the current user's name on a form using the new userProfileLookup function.

Is there any documentation for this new feature. I've tried using: userProfileLookup(Current User, "DisplayName") but that just returns a blank field. (I also tried "displayName", "Display Name" but no joy there either.

Cheers,

Iain