I am currently working with a client developing a solution that can be used to integrate Form Services from a SharePoint 2007 large farm to a SharePoint 2010 large farm. The requirement is to allow the users on the extranet to enter information for a business process and then have the intranet users work with that information with another process.
First, I developed a solution matrix with a list of 3 main options for this solution and based on the time, budget and team skill set, the business selected the InfoPath solution.
For this solution, first you create an InfoPath form with all the fields and data that you need and deploy it as web form on a form library in MOSS s007 (We used InfoPath 2010 to develop the form). Then on the submit button, instead of entering the URL of the extranet farm, you can enter the URL of the Intranet MOSS 2010 farm. Of course, we worked with the security team to secure that connection with IP to IP and service account security.
Also, select the XML option when adding the Submit action to the InfoPath form. This way you can use the XSD.exe command in InfoPath to generate the C# class that matches your xml schema.
Once the information is in a Form Library in SharePoint 2010-Intranet, you can use the generated C# code and a custom WF workflow to start the Intranet process and deliver the information you need for the second process.
Note: Remember that this type of integration will require that you purchase Internet licenses for the SharePoint 2010 Intranet farm since the information is coming from the extranet.