Last week I had a customer that used InfoPath extensively for basic data capture. The forms themselves were quite basic. Most had a couple of data connections to SharePoint lists (for drop-down values), as well as the main Submit data connection. Modifying each of these forms involved migrating each of the lookup lists to the new SharePoint environment, creating the destination Forms Library to hold the submitted forms, modifying each of the data connections in InfoPath to point to these lists and libraries, and finally Publishing the form to the new location.
Of bigger concern was the fact that there were hundreds (if not thousands) of data files (i.e. .xml files containing submitted data). As you may or may not know, submitted InfoPath documents have a processing instruction at the top of the XML, which tells Windows that it is an InfoPath document, as well as where to get the InfoPath XSN template to load.
Fortunately, MOSS form libraries now have a new default view called 'Relink Documents'. By using this view, you can select each of the existing documents and relink them to the new template. Below is a screenshot: