"The tooltips are a user interface element of the Gravity Forms admin and not the forms themselves. It is something we'd like to add in the future, but it is not currently a built in feature of the forms. So there is no built in functionality in Gravity Forms to add tooltips.
If you wanted to implement tooltips on your forms you could do so, but you would have to implement it as a customization using an existing tooltip jQuery script. It's not something Gravity Forms itself is going to be able to provide you functionality for."
Come on... Let's add this one to the feature set... You're already doing it in the admin tool so share the code with the rest of us... :-)