I just came across this great article on the home page of the MSDN site today: Digitally Signing Data in InfoPath 2003 . Since we're covering InfoPath SP1 enhancements in our MSDN Events these days, I thought it would be useful for attendees (or anyone else interested in InfoPath for that matter).

The article really goes in-depth into using digital signatures not only as part of filling out form data, but also for digitally signing your form templates that use manage code to get them trusted. Very useful!