InfoPath Dev

I’m trying to find a way to get a form opened in the InfoPath client to submit back into the same SharePoint library from where the user clicked “New” to create it. I’d like to calculate this value in the code-behind on the form (as opposed to using static or named data connections) because I don’t know all the libraries where the form will be ...

You need to create a rule to update the value of your username field whenever the form is opened. Go to "Tools / Form Options / Open and Save" and add this rule: Action: =fx Set a field's value, Field: @username, Value: username(). You should be good to go.